Screening method for the identification of agents capable of activating CD4+CD25+ regulatory T-cells through interactions with the HIV-1 GP120 binding site on CD4

ABSTRACT

The present invention relates specific activation of a regulatory T cell via a specific CD4 epitope and uses thereof, e.g. for the treatment of an autoimmune disease or an allergy or asthma or graft rejection or tolerance induction.

This application is the national phase entry under 35 U.S.C. §371 of International Application No. PCT/EP2008/051144, filed Jan. 30, 2008, which claims priority to European Patent Applications No. 07101604.2, filed Feb. 1, 2007 and 07122424.0, filed Dec. 5, 2007, which are hereby incorporated by reference in their entireties.

INTRODUCTION

Asthma, an allergic disease, transplant rejection and an autoimmune disease have one fundamental principle in common, they all are triggered by an imbalanced immune system which reacts hyperactive against a specific exogenic and/or endogenic challenge and therewith contributes significantly to the disease status.

It is generally accepted that such aberrations of the immune system have a common pathophysiological mechanism triggered by hyper-responsive effector T cells playing a central role in immune reactivity. Effector T cell-directed immunomodulation therefore is the key to successful treatment of asthma, an autoimmune condition, prevention of graft vs. host disease (GVHD) and prevention of graft rejection.

T lymphocytes, designated as regulatory T cells (“Treg cells”) control immune responses by suppressing the effector function of CD4⁺ T cells and CD8⁺ T cells (Shevach 2002). Different subsets of Treg cells have been described. These include but are not limited to (i) CD4⁺CD25⁺ Treg cells—also designated as “naturally occurring Treg cells” (Sakaguchi 2005), (ii) Tr1 (Roncarolo et al. 2001) and (iii) Th3 (Weiner 2001). Tr1 and Th3 are induced in the periphery, whereas CD4⁺CD25⁺ Treg cells develop in the thymus and constitute 5-10% of peripheral CD4⁺ T cells in healthy man. At least in vitro these cells are anergic, produce minimal amounts of cytokines and exert their suppressive effects only upon stimulation and in a strictly cell-contact dependent manner. Tr1 and Th3 exert their suppressive activity by production of IL-10 and TGF-beta, respectively (Shevach 2002).

Genetic defects that primarily affect Treg cell development or function should cause autoimmune and inflammatory aberrations. IPEX syndrome (immunodysregulation, polyendo-crinopathy and enteropathy, X-linked), a rare recessive disorder in humans is caused by a mutation in the gene of the transcription factor FOXP3 and subsequent absence of Treg cells. IPEX shows aggressive autoimmunity, severe eczema, elevated IgE levels, eosinophilia and food allergies and early death (Fontenot and Rudensky 2005).

Data from the literature show that Treg cells play an important role in asthma and autoimmune diseases and have a potential for treatment of GVHD and therewith transplantation tolerance (Robinson 2004, Sakaguchi 2005).

Therefore, attempts have been started to use Treg cells as a therapeutic agent for patients with established autoimmune disease (Horwitz et al. 2003). It is believed that said patients lack sufficient Treg cells or do have impaired Treg cell function resulting in misdirected and uncontrolled effector T cell activity. The previous thinking for solving this problem is administering Treg cells to a said patient. Since Treg cells are rare in peripheral blood clinical application of human Treg cells depends on highly expensive ex vivo expansion of Treg cells (Hoffmann et al. 2004, Horwitz et al. 2003, Tang et al. 2003, Zheng et al. 2004). Bluestone and Tang went one step further: They are trying to solve the problem by not only increasing the amount of Treg cells for therapy but enhancing suppressive activity of Treg cells by activating Treg cells via triggering of the T cell receptor (TCR) by an anti-CD3 antibody (Bluestone and Tang 2004). This approach resembles by far no Treg cell specific activation as anti-CD3 activates all T cell receptor-expressing cells which bears the obstacle that anti-CD3 treatment induces effector T cell function probably leading to uncontrolled proliferation and non-specific pro-inflammatory cytokine production and exaggeration of pathology. To circumvent this unwanted triggering of effector T cells Treg cells have to be highly purified and activated ex vivo with anti-CD3 which again is a highly expensive and laborious procedure. In addition, the absence of a Treg cell specific marker makes it difficult to achieve high purity of Treg cells.

Therefore, it is a primary goal to identify a substance which can activate Treg cells specifically without stimulating the immune system any further and therefore would provide a basis for a direct in vivo application without money consuming ex vivo treatments.

There is some information in the prior art how Treg cells possibly can be activated, e.g. nonspecifically via CD3 (Thornton and Shevach 1998), or via CD28/B7 pathway (Shevach 2002, Bluestone and Tang 2004, Hunig and Dennehy 2005), or via CD4 (WO04083247). So far all this solutions do not result in a specific Treg cell activation.

DESCRIPTION OF THE INVENTION

The present invention bases on the new finding that a specific epitope of CD4 triggers activation of Treg cells. Said epitope overlaps with the known HIV-1 gp120-binding site but surprisingly binding to this site causes Treg cell activation. This finding was totally unexpected for the following reasons: Until now Treg cell activation via CD4 was attributed to a different epitope to which the monoclonal antibody BF5 (WO04083247) binds. —Carriere et al., 1995 have investigated that the binding site of BF5 on CD4 is completely independent of the HIV-1 gp120-binding site. —Unexpectedly, despite reports in the literature on direct anergizing and blocking of CD4 on T cell function by HIV-1 gp120 (Diamond et al. 1988), we found an activating property of HIV-1 gp120 on CD4 of Treg cells.

The present invention discloses a physiologically active CD4 epitope on a Treg cell which triggers suppressive activity of a Treg cell. The epitope of the present invention has been identified as a region on the human CD4 protein (SEQ ID NO.: 2) spanning amino acid position No. 54 to 84 of SEQ ID NO.:2. Those 31 amino acids are explicitly given in SEQ ID NO.:1.

A preferred peptide which is a CD4 fragment according to the present invention is selected from a group consisting of an isolated peptide spanning amino acid No. 1-31 of SEQ ID NO 1, No. 26 to 458 of SEQ ID NO.: 2, No. 26 to 419 of SEQ ID NO.:2, No. 26 to 207 of SEQ ID NO.: 2, No. 26 to 131 of SEQ ID NO.: 2 and No. 46 to 89 of SEQ ID NO.: 2. All said peptides are additionally characterized in that they all do harbor the critical amino acid Phenylalanine at residue 68 of SEQ ID NO.: 2.

The finding that the epitope given in SEQ ID NO.:1 is a key to activate a Treg cell provides a basis for several uses, e.g.:

Methods for identification of a substance which can activate a regulatory T cell (Treg cell). Such a substance is designated “Treg cell activator” of the present invention which is useful for the treatment of a disease of the invention which is a disease in which increase of activated regulatory T cells (Treg cells) can improve clinical picture wherein such a disease is (i) a non-autoimmune inflammatory disease: asthma, allergic asthma, respiratory allergy, allergic rhinoconjunctivitis, allergic alveolitis, contact allergy, atopic dermatitis, neurodermatitis, food allergy, graft-versus-host disease, non-autoimmune inflammatory bowel disease, acute respiratory distress syndrome, acute inflammatory pancreatitis, burns, wound healing, skin scarring disorders, sarcoidosis, Behcet's disease or Sweet's syndrome; (ii) an autoimmune inflammatory disease: rheumatoid arthritis, rheumatic fever, systemic lupus erythematosus, ulcerative colitis, Crohn's disease, autoimmune inflammatory bowel disease, diabetes type I, gastritis, autoimmune atrophic gastritis, autoimmune hepatitis, Hashimoto's thyroiditis, thyreoiditis, multiple sclerosis, myasthenia gravis, autoimmune haemolytic anemia, Addison's disease, scleroderma, Goodpasture's syndrome, Guillain-Barre syndrome, Graves' disease, glomerulonephritis, psoriasis, pemphigus vulgaris, pemphigoid, vitiligo, idiopathic leukopenia, Sjogren's syndrome or Wegener's granulomatosis; (iii) an inflammatory disease due to organ transplantation; (iv) a bone marrow transplantation; or (v) a disease due to exogenously administered self or exogenously administered non-autologous recombinant polypeptide.

A “substance” of the present invention can be used in a method according to the present invention. The meaning of the term substance according to the present invention includes but is not limited to a peptide, a scaffolded peptide, an antibody, a fragment of an antibody, a nucleic acid molecule, a ribozyme, an organic compound or an inorganic compound.

In a second aspect, the new epitope serves as the basis for the synthesis of a new tool which can be used e.g. in a competition assay or screening assay according to the present invention for determining whether a substance can activate a regulatory T cell (Treg cell) via interaction with the epitope as set forth in SEQ ID No.:1. Such a tool is a peptide of the present invention which is an isolated peptide spanning amino acid No. 1-31 of SEQ ID NO 1, or No. 26 to 458 of SEQ ID NO.: 2, or No. 26 to 419 of SEQ ID NO.:2, or No. 26 to 207 of SEQ ID NO.: 2, or No. 26 to 131 of SEQ ID NO.: 2 or No. 46 to 89 of SEQ ID NO.: 2, or is an isolated peptide spanning amino acid No. 1 to 31 of SEQ ID NO.: 1 and having additional up-stream and/or downstream amino acids with the prerequisite that the additional amino acids do not hinder binding of a substance to the amino acid stretch as set forth in SEQ ID No.:1. A preferred peptide according to the present invention consist of the peptide as set forth in SEQ ID NO.:1 and additionally consist of an additional up-stream amino acid or amino acid stretch which is selected from a group consisting of the amino acid or amino acid stretch as set forth in SEQ ID NO.: 2 at position 53, at position 52-53, at position 51-53, at position 50-53, at position 49-53, at position 48-53, at position 47-53, at position 46-53, at position 45-53, at position 44-53, at position 43-53, at position 42-53, at position 41-53, at position 40-53, at position 39-53, at position 38-53, at position 37-53, at position 36-53, at position 35-53, at position 34-53, at position 33-53, at position 32-53, at position 31-53, at position 30-53, at position 29-53, at position 28-53, at position 27-53, at position 26-53, at position 25-53, at position 24-53, at position 23-53, at position 22-53, at position 21-53, at position 20-53, at position 19-53, at position 18-53, at position 17-53, at position 16-53, at position 15-53, at position 14-53, at position 13-53, at position 12-53, at position 11-53, at position 10-53, at position 9-53, at position 8-53, at position 7-53, at position 6-53, at position 5-53, at position 4-53, at position 3-53, at position 2-53, and at position 1-53.

A further preferred peptide according to the present invention consists of the peptide which is mentioned as “preferred peptide” in the paragraph above and additionally consists of at least one additional downstream amino acid as given in SEQ ID NO.: 2 at position 85, or additionally consists of amino acids as given in SEQ ID NO.:2 at position 85 to n, wherein n is an integer between 86-458, i.e. position 85 to 86, 85 to 87, 85 to 88, 85 to 89, 85 to 90, 85 to 91, 85 to 92, 85 to 93, 85 to 94, 85 to 95, 85 to 96, 85 to 97, 85 to 98, 85 to 99, 85 to 100, 85 to 101, 85 to 102, 85 to 103, 85 to 104, 85 to 105, 85 to 106, 85 to 107, 85 to 108, 85 to 109, 85 to 110, 85 to 111, 85 to 112, 85 to 113, 85 to 114, 85 to 115, 85 to 116, 85 to 117, 85 to 118, 85 to 119, 85 to 120, 85 to 121, 85 to 122, 85 to 123, 85 to 124, 85 to 125, 85 to 126, 85 to 127, 85 to 128, 85 to 129, 85 to 130, 85 to 131, 85 to 132, 85 to 133, 85 to 134, 85 to 135, 85 to 136, 85 to 137, 85 to 138, 85 to 139, 85 to 140, 85 to 141, 85 to 142, 85 to 143, 85 to 144, 85 to 145, 85 to 146, 85 to 147, 85 to 148, 85 to 149, 85 to 150, 85 to 151, 85 to 152, 85 to 153, 85 to 154, 85 to 155, 85 to 156, 85 to 157, 85 to 158, 85 to 159, 85 to 160, 85 to 161, 85 to 162, 85 to 163, 85 to 164, 85 to 165, 85 to 166, 85 to 167, 85 to 168, 85 to 169, 85 to 170, 85 to 171, 85 to 172, 85 to 173, 85 to 174, 85 to 175, 85 to 176, 85 to 177, 85 to 178, 85 to 179, 85 to 180, 85 to 181, 85 to 182, 85 to 183, 85 to 184, 85 to 185, 85 to 186, 85 to 187, 85 to 188, 85 to 189, 85 to 190, 85 to 191, 85 to 192, 85 to 193, 85 to 194, 85 to 195, 85 to 196, 85 to 197, 85 to 198, 85 to 199, 85 to 200, 85 to 201, 85 to 202, 85 to 203, 85 to 204, 85 to 205, 85 to 206, 85 to 207, 85 to 208, 85 to 209, 85 to 210, 85 to 211, 85 to 212, 85 to 213, 85 to 214, 85 to 215, 85 to 216, 85 to 217, 85 to 218, 85 to 219, 85 to 220, 85 to 221, 85 to 222, 85 to 223, 85 to 224, 85 to 225, 85 to 226, 85 to 227, 85 to 228, 85 to 229, 85 to 230, 85 to 231, 85 to 232, 85 to 233, 85 to 234, 85 to 235, 85 to 236, 85 to 237, 85 to 238, 85 to 239, 85 to 240, 85 to 241, 85 to 242, 85 to 243, 85 to 244, 85 to 245, 85 to 246, 85 to 247, 85 to 248, 85 to 249, 85 to 250, 85 to 251, 85 to 252, 85 to 253, 85 to 254, 85 to 255, 85 to 256, 85 to 257, 85 to 258, 85 to 259, 85 to 260, 85 to 261, 85 to 262, 85 to 263, 85 to 264, 85 to 265, 85 to 266, 85 to 267, 85 to 268, 85 to 269, 85 to 270, 85 to 271, 85 to 272, 85 to 273, 85 to 274, 85 to 275, 85 to 276, 85 to 277, 85 to 278, 85 to 279, 85 to 280, 85 to 281, 85 to 282, 85 to 283, 85 to 284, 85 to 285, 85 to 286, 85 to 287, 85 to 288, 85 to 289, 85 to 290, 85 to 291, 85 to 292, 85 to 293, 85 to 294, 85 to 295, 85 to 296, 85 to 297, 85 to 298, 85 to 299, 85 to 300, 85 to 301, 85 to 302, 85 to 303, 85 to 304, 85 to 305, 85 to 306, 85 to 307, 85 to 308, 85 to 309, 85 to 310, 85 to 311, 85 to 312, 85 to 313, 85 to 314, 85 to 315, 85 to 316, 85 to 317, 85 to 318, 85 to 319, 85 to 320, 85 to 321, 85 to 322, 85 to 323, 85 to 324, 85 to 325, 85 to 326, 85 to 327, 85 to 328, 85 to 329, 85 to 330, 85 to 331, 85 to 332, 85 to 333, 85 to 334, 85 to 335, 85 to 336, 85 to 337, 85 to 338, 85 to 339, 85 to 340, 85 to 341, 85 to 342, 85 to 343, 85 to 344, 85 to 345, 85 to 346, 85 to 347, 85 to 348, 85 to 349, 85 to 350, 85 to 351, 85 to 352, 85 to 353, 85 to 354, 85 to 355, 85 to 356, 85 to 357, 85 to 358, 85 to 359, 85 to 360, 85 to 361, 85 to 362, 85 to 363, 85 to 364, 85 to 365, 85 to 366, 85 to 367, 85 to 368, 85 to 369, 85 to 370, 85 to 371, 85 to 372, 85 to 373, 85 to 374, 85 to 375, 85 to 376, 85 to 377, 85 to 378, 85 to 379, 85 to 380, 85 to 381, 85 to 382, 85 to 383, 85 to 384, 85 to 385, 85 to 386, 85 to 387, 85 to 388, 85 to 389, 85 to 390, 85 to 391, 85 to 392, 85 to 393, 85 to 394, 85 to 395, 85 to 396, 85 to 397, 85 to 398, 85 to 399, 85 to 400, 85 to 401, 85 to 402, 85 to 403, 85 to 404, 85 to 405, 85 to 406, 85 to 407, 85 to 408, 85 to 409, 85 to 410, 85 to 411, 85 to 412, 85 to 413, 85 to 414, 85 to 415, 85 to 416, 85 to 417, 85 to 418, 85 to 419, 85 to 420, 85 to 421, 85 to 422, 85 to 423, 85 to 424, 85 to 425, 85 to 426, 85 to 427, 85 to 428, 85 to 429, 85 to 430, 85 to 431, 85 to 432, 85 to 433, 85 to 434, 85 to 435, 85 to 436, 85 to 437, 85 to 438, 85 to 439, 85 to 440, 85 to 441, 85 to 442, 85 to 443, 85 to 444, 85 to 445, 85 to 446, 85 to 447, 85 to 448, 85 to 449, 85 to 450, 85 to 451, 85 to 452, 85 to 453, 85 to 454, 85 to 455, 85 to 456, 85 to 457, or 85 to 458.

Additionally, the finding that the epitope given in SEQ ID NO.:1 is a key to activate a Treg cell is a link between two different up to now unrelated technical fields, namely that of (a) HIV-1 related diseases with (b) diseases according to the present invention e.g autoimmune disease, allergy, asthma, graft rejection and a diseases due to lacking immunotolerance caused by organ transplantation or by therapeutical administration of a non-self or self biological entity to a human in need thereof and therewith allows a bundle of new uses as explained in the following:

The epitope given in SEQ ID NO.:1 is not only a further epitope which can be used to activate Treg cells. HIV-1 gp120 interacts with CD4 of T cells and therewith enables virus entry into a CD4⁺ cell (Klatzmann et al. 1984). The finding that epitope given in SEQ ID NO.:1 harbors the high affinity binding site on CD4 to which human immune deficiency virus 1 (HIV-1) glycoprotein gp120 binds (Jameson et al. 1988, Arthos et al. 1989) offers a further advantage. It provides the basis to bring together the findings of two different unrelated technical fields that of i.e. HIV-1 related diseases with diseases according to the present invention.

To alleviate the worldwide HIV-1 problem many efforts have been made to identify a substance which is able to inhibit HIV-1 entry into a CD4⁺ cell. As a result thereof, so called HIV-1 attachment or entry inhibitors are known in the art.

The keyhole which allows HIV-1 to enter the cell can be used as the keyhole to activate Treg cells. Therefore, substances known in the art to interfere with HIV-1 attachment and cell entry (Markovic and Clouse 2004, Castagna et al. 2005), like e.g. HIV-1 gp120 itself, derivatives thereof, peptidomimetics, antibodies, aptamers or any low molecular weight (LMW) compound directed against the binding site of HIV-1 gp120 on CD4 could possibly be useful to activate a Treg cell and therewith can be useful for the treatment of a disease according to the present invention (HIV-1 gp120 is well-known in the art and its amino acid sequence as well as the respective gene has been published since years (Muesing et al. 1985, Starcich et al. 1986, Jeffs et al. 1996). Additionally, methods for producing HIV-1 gp120 are known (Lasky et al. 1986, Leonard et al. 1990, Culp et al. 1991, Jeffs et al. 1996).

A substance which can interfere with HIV-1 attachment and/or cell entry is commonly named HIV-1 attachment inhibitor or entry inhibitor. Such a substance, do either bind to (i) HIV-1, or (ii) to CD4, or (iii) HIV-1 and CD4 or (iv) co-receptor e.g. CCR5 or CXCR4. Such an inhibitor can be according to the present invention useful for the treatment of diseases according to the present invention like e.g. an autoimmune disease, an allergy, asthma or GVHD if it exerts property (ii) or (iii) and activates a Treg cell. To determine whether such an inhibitor can be useful for a said disease the present invention discloses several assays which allow to determine whether a substance identified in the technical field of HIV-1 research to interfere with HIV-1 attachment and/or cell entry can be useful in the other above-mentioned technical fields like that of autoimmune diseases or allergies or asthma or organ transplantation. Therefore, the present invention teaches a short cut for identifying a substance which can be useful for the treatment of a disease according to the present invention.

Identification of a substance which can be used as a medicament in a specific disease usually depends on resource consuming high through put screenings (HTS). Determination whether a substance can activate a Treg cell currently depends on a cellular assay comprising a Treg cell. Since Treg cells can only be provided in small amounts large screening campaigns or even an HTS therewith are not feasible today. The teaching of the present invention allows to circumvent this obstacles since the present invention allows to pre-select substances which possible can activate a Treg cell. According to the present invention an appropriate pre-selected substance is (i) proven to interact at least with epitope (SEQ ID NO.:1), and/or is (ii) known from HIV-1 research as HIV-1 attachment inhibitor or entry inhibitor or synthetic mimetics of the CD4 binding site of HIV-1 gp120.

It is state of the art to determine whether a substance can interact with a given peptide and therewith a given epitope even in an HTS format. Concerning the present invention this can be performed for example in an in vitro competition type assay comprising a peptide spanning at least amino acids as set forth in SEQ ID NO.: 1 mixed with an unlabeled substance to be tested and subsequently with a labeled substance which is known to bind the peptide (e.g. HIV-1 gp120) under conditions which allow binding of the peptide with the labeled substance. A substance which interact with the peptide will compete with the labeled substance and is identifiable by a rendered readout, which can be performed e.g. by measuring the bound or free labeled substance.

Such a type of assay for determining whether a substance can interact with a specific peptide, i.e. epitope is not restricted to in vitro assays since cellular assays for achieving such an information on a substance or other in vitro formats are well known in the art and broadly used.

In one embodiment the present invention concerns a method for determining whether a substance which can interfere with the interaction of HIV-1 gp120 with CD4 can be useful for positively influence a disease in which increase of activated regulatory T cells (Treg cells) can improve clinical picture comprising:

-   -   (a) providing a solution comprising a Treg cell, wherein a Treg         cell is preferably a CD4⁺CD25⁺ Treg cell or a Tr1 cell or a Th3         cell. Said solution does more preferably comprise additionally         an inactivated syngenic CD3-depleted PBMC (peripheral blood         mononuclear cell which has preferably been inactivated via         irradiation or via mitomycin C) or a dendritic cell (DC) and an         allogeneic CD8+ T cell or an allogeneic CD4+ T cell,     -   (b) adding a substance to be tested under conditions which allow         interaction of the substance with a Treg cell,     -   (c) measuring whether a Treg cell has been activated, wherein an         activated Treg cell identifies the substance as a Treg cell         activator.         -   Said measuring can be performed using a suitable read-out             system such as:         -   (i) measuring whether a CD8⁺ T cell has been             suppressed—which preferably can be determined by measuring             inhibited proliferation of the CD8⁺ T cell or by measuring             reduced CD25 expression of the CD8⁺ T cell, or by measuring             inhibited cytokine production of the CD8⁺ T cell wherein a             suitable cytokine is IFNγ or IL2, or TNFα—wherein a             suppressed CD8⁺ T cell identifies an activated Treg cell and             therewith identifies the substance as a Treg cell activator,             or by         -   (ii) measuring whether a CD4⁺ T cell has been             suppressed—which preferably can be determined by measuring             inhibited proliferation of the CD4⁺ T cell or by measuring             reduced CD25 expression of the CD4⁺ T cell, or by measuring             inhibited cytokine production of the CD4⁺ T cell wherein a             suitable cytokine is IFNγ or IL2, or TNFα—wherein a             suppressed CD4⁺ T cell identifies an activated Treg cell and             therewith identifies the substance as a Treg cell activator,             or by         -   (iii) measuring the amount of intracellular cAMP (i.e.             cytosolic cAMP) and wherein an increased amount of             intracellular cAMP is indicative for an activated Treg cell             and therewith identifies the substance as a Treg cell             activator.

A disease according to the method above in which increase of activated regulatory T cells (Treg cells) can improve clinical picture is (i) a non-autoimmune inflammatory disease: asthma, allergic asthma, respiratory allergy, allergic rhinoconjunctivitis, allergic alveolitis, contact allergy, atopic dermatitis, neurodermatitis, food allergy, graft-versus-host disease, non-autoimmune inflammatory bowel disease, acute respiratory distress syndrome, acute inflammatory pancreatitis, burns, wound healing, skin scarring disorders, sarcoidosis, Behcet's disease or Sweet's syndrome; (ii) an autoimmune inflammatory disease: rheumatoid arthritis, rheumatic fever, systemic lupus erythematosus, ulcerative colitis, Crohn's disease, autoimmune inflammatory bowel disease, diabetes type I, gastritis, autoimmune atrophic gastritis, autoimmune hepatitis, Hashimoto's thyroiditis, thyreoiditis, multiple sclerosis, myasthenia gravis, autoimmune haemolytic anemia, Addison's disease, scleroderma, Goodpasture's syndrome, Guillain-Barre syndrome, Graves' disease, glomerulonephritis, psoriasis, pemphigus vulgaris, pemphigoid, vitiligo, idiopathic leukopenia, Sjogren's syndrome or Wegener's granulomatosis; (iii) an inflammatory disease due to organ transplantation; (iv) a bone marrow transplantation; or (v) a disease due to exogenously administered self or exogenously administered non-autologous recombinant polypeptide.

As the readout systems as mentioned in (i) and (ii) above are methods in which several steps have to be performed a specific new test system has been invented to determine in only one step whether a Treg cell has been activated which is mentioned in (iii) above. Basing on the surprising finding that the activation status of a Treg cell strongly correlates with the amount of intracellular cAMP the present invention provides for a specific method for determining whether a Treg cell has been activated which comprises:

-   -   (a) providing a first solution comprising a Treg cell,     -   (b) providing a second solution comprising a Treg cell,     -   (c) manipulation the first solution by adding at least a test         substance,     -   (d) determining the amount of intracellular cAMP of the first         and the second solution wherein an increased amount of         intracellular cAMP of the first solution is indicative for an         activated Treg cell.

In a more preferred method the solution of (a) does not only contain a Treg cell but also an inactivated syngenic CD3-depleted PBMC (peripheral blood mononuclear cell) or a dendritic cell (DC) and an allogeneic CD8⁺ T cell or an allogeneic CD4⁺ T cell. These cells when combined in one solution with a activated Treg cell do additionally increase intracellular cAMP amount and therewith lead to a more sensitive readout system.

In a further embodiment the present invention concerns a method for determining whether a substance can activate a Treg cell via interaction with the HIV-1 gp120-binding site of CD4, comprising:

-   -   (a) pre-selecting a substance which can interact with the HIV-1         gp120-binding site of CD4 (for a method for pre-selection please         see below),     -   (b) providing a solution comprising a Treg cell wherein a Treg         cell is preferably a CD4⁺CD25⁺ Treg cell or a Tr1 cell or a Th3         cell. Said solution does more preferably comprise additionally         an inactivated syngenic CD3-depleted PBMC (peripheral blood         mononuclear cell) which has preferably been inactivated via         irradiation or via mitomycin C) or a dendritic cell (DC) and an         allogeneic CD8+ T cell or an allogeneic CD4+ T cell,     -   (c) adding a pre-selected substance according to (a) under         conditions which allow interaction of the substance with a Treg         cell,     -   (d) measuring whether a Treg cell has been activated, wherein an         activated Treg cell identifies the substance as a Treg cell         activator. Said measuring can be performed using a suitable         read-out system such as:

-   (i) measuring whether a CD8⁺ T cell has been suppressed—which     preferably can be determined by measuring inhibited proliferation of     the CD8⁺ T cell or by measuring reduced CD25 expression of the CD8⁺     T cell, or by measuring inhibited cytokine production of the CD8⁺ T     cell wherein a suitable cytokine is IFNγ or IL2, or TNFα—wherein a     suppressed CD8⁺ T cell identifies an activated Treg cell and     therewith identifies the substance as a Treg cell activator, or by

-   (ii) measuring whether a CD4⁺ T cell has been suppressed—which     preferably can be determined by measuring inhibited proliferation of     the CD4⁺ T cell or by measuring reduced CD25 expression of the CD4⁺     T cell, or by measuring inhibited cytokine production of the CD4⁺ T     cell wherein a suitable cytokine is IFNγ or IL2, or TNFα—wherein a     suppressed CD4⁺ T cell identifies an activated Treg cell and     therewith identifies the substance as a Treg cell activator, or by

-   (iii) measuring the amount of intracellular cAMP and wherein an     increased amount of intracellular cAMP is indicative for an     activated Treg cell and therewith identifies the substance as a Treg     cell activator.

The present invention also provides for a method which allow to identify a substance which can interact with the HIV-1 gp120-binding site of CD4 and therewith can be used for pre-selecting a substance which can interact with the HIV-1 gp120-binding site of CD4. The method comprises:

-   -   (a) providing a first solution comprising CD4,     -   (b) providing a second solution comprising CD4,     -   (c) adding to the first solution a substance to be tested and         HIV-1 gp120 under conditions which allow binding of HIV-1 gp120         with CD4,     -   (d) adding to the second solution HIV-1 gp120 under conditions         like (c) allowing binding of HIV-1 gp120 with CD4,     -   (e) measuring in the first and in the second solution whether         the HIV-1 gp120 has bound to the CD4 wherein a reduced amount of         bound HIV-1 gp120 in the first solution indicates that the         substance can interact with HIV-1 gp120-binding site of CD4.

This pre-selecting method can additionally be performed according to the present invention if instead of CD4 a peptide is used which comprises the amino acid stretch as set forth in SEQ ID NO. 1 or instead of CD4 a peptide is used as set forth in SEQ ID NO.:1. In a more preferred method according to the present invention instead of HIV-1 gp120 a peptide is used selected from a group consisting of a peptide comprising the amino acid sequence as set forth in SEQ ID NO.: 3, SEQ ID NO.: 4, SEQ ID NO.: 5, SEQ ID NO.: 6, SEQ ID NO.: 7, SEQ ID NO.: 8, SEQ ID NO.: 9, and SEQ ID NO.: 10 or a peptide is used selected from a group consisting of a peptide consisting of the amino acid sequence as set forth in SEQ ID NO.: 3, SEQ ID NO.: 4, SEQ ID NO.: 5, SEQ ID NO.: 6, SEQ ID NO.: 7, SEQ ID NO.: 8, SEQ ID NO.: 9, and SEQ ID NO.: 10.

In a further embodiment the present invention concerns a method for determining whether a substance can activate a regulatory T cell (Treg) via interaction with the epitope as set forth in SEQ ID NO: 1 comprising:

-   -   (a) providing a first solution comprising a Treg cell, wherein a         Treg cell is preferably a CD4⁺CD25⁺ Treg cell or a Tr1 cell or a         Th3 cell. Said solution does more preferably comprise         additionally an inactivated syngenic CD3-depleted PBMC         (peripheral blood mononuclear cell which has preferably been         inactivated via irradiation or via mitomycin C) or a dendritic         cell (DC) and an allogeneic CD8+ T cell or an allogeneic CD4+ T         cell,     -   (b) adding a substance to be tested under conditions which allow         interaction of the substance with a Treg cell,     -   (c) measuring whether a Treg cell of the first solution has been         activated,     -   (d) providing a second solution comprising a Treg cell, wherein         a Treg cell is preferably a CD4⁺CD25⁺ Treg cell or a Tr1 cell or         a Th3 cell. Said solution does more preferably comprise         additionally an inactivated syngenic CD3-depleted PBMC         (peripheral blood mononuclear cell which has preferably been         inactivated via irradiation or via mitomycin C) or a dendritic         cell (DC) and an allogeneic CD8+ T cell or an allogeneic CD4+ T         cell,     -   (e) adding the substance to be tested and a peptide comprising         an amino acid sequence as set forth in SEQ ID NO: 1 under         conditions like (b),     -   (f) measuring whether a Treg cell of the second solution has         been activated,         -   Said measuring can be performed using a suitable read-out             system such as:         -   (i) measuring whether a CD8⁺ T cell has been             suppressed—which preferably can be determined by measuring             inhibited proliferation of the CD8⁺ T cell or by measuring             reduced CD25 expression of the CD8⁺ T cell, or by measuring             inhibited cytokine production of the CD8⁺ T cell wherein a             suitable cytokine is IFNγ or IL2, or TNFα—wherein a             suppressed CD8⁺ T cell identifies an activated Treg cell and             therewith identifies the substance as a Treg cell activator,             or by         -   (ii) measuring whether a CD4⁺ T cell has been             suppressed—which preferably can be determined by measuring             inhibited proliferation of the CD4⁺ T cell or by measuring             reduced CD25 expression of the CD4⁺ T cell, or by measuring             inhibited cytokine production of the CD4⁺ T cell wherein a             suitable cytokine is IFNγ or IL2, or TNFα—wherein a             suppressed CD4⁺ T cell identifies an activated Treg cell and             therewith identifies the substance as a Treg cell activator,             or by         -   (iii) measuring the amount of intracellular cAMP and wherein             an increased amount of intracellular cAMP is indicative for             an activated Treg cell and therewith identifies the             substance as a Treg cell activator;     -   (g) comparing results obtained from (c) with those obtained         from (f) wherein a reduced activation of (f) identifies the         substance as a Treg cell activator which activates a Treg cell         via interaction with the epitope as set forth in SEQ ID NO: 1.

In a more preferred method in step (e) of above mentioned method the peptide used is selected from a group consisting of an isolated peptide spanning amino acid No. 1-31 of SEQ ID NO 1, No. 26 to 458 of SEQ ID NO.: 2, No. 26 to 419 of SEQ ID NO.:2, No. 26 to 207 of SEQ ID NO.: 2, No. 26 to 131 of SEQ ID NO.: 2 and No. 46 to 89 of SEQ ID NO.: 2 or the peptide used is an isolated peptide spanning amino acid No. 1 to 31 of SEQ ID NO.: 1 and having additional up-stream and/or downstream amino acids with the prerequisite that the additional amino acids do not hinder binding of a substance to the amino acid stretch as set forth in SEQ ID No.:1. Said additional up-stream amino acid or amino acid stretch is preferably selected from a group consisting of the amino acid or amino acid stretch as set forth in SEQ ID NO.: 2 at position 53, at position 52-53, at position 51-53, at position 50-53, at position 49-53, at position 48-53, at position 47-53, at position 46-53, at position 45-53, at position 44-53, at position 43-53, at position 42-53, at position 41-53, at position 40-53, at position 39-53, at position 38-53, at position 37-53, at position 36-53, at position 35-53, at position 34-53, at position 33-53, at position 32-53, at position 31-53, at position 30-53, at position 29-53, at position 28-53, at position 27-53, at position 26-53, at position 25-53, at position 24-53, at position 23-53, at position 22-53, at position 21-53, at position 20-53, at position 19-53, at position 18-53, at position 17-53, at position 16-53, at position 15-53, at position 14-53, at position 13-53, at position 12-53, at position 11-53, at position 10-53, at position 9-53, at position 8-53, at position 7-53, at position 6-53, at position 5-53, at position 4-53, at position 3-53, at position 2-53, and at position 1-53. A more preferred peptide does additionally comprise downstream one or more amino acids as set forth in SEQ ID NO.: 2 at position 85, or at position 85 to n, wherein n is an integer between 86-458, i.e. position 85 to 86, 85 to 87, 85 to 88, 85 to 89, 85 to 90, 85 to 91, 85 to 92, 85 to 93, 85 to 94, 85 to 95, 85 to 96, 85 to 97, 85 to 98, 85 to 99, 85 to 100, 85 to 101, 85 to 102, 85 to 103, 85 to 104, 85 to 105, 85 to 106, 85 to 107, 85 to 108, 85 to 109, 85 to 110, 85 to 111, 85 to 112, 85 to 113, 85 to 114, 85 to 115, 85 to 116, 85 to 117, 85 to 118, 85 to 119, 85 to 120, 85 to 121, 85 to 122, 85 to 123, 85 to 124, 85 to 125, 85 to 126, 85 to 127, 85 to 128, 85 to 129, 85 to 130, 85 to 131, 85 to 132, 85 to 133, 85 to 134, 85 to 135, 85 to 136, 85 to 137, 85 to 138, 85 to 139, 85 to 140, 85 to 141, 85 to 142, 85 to 143, 85 to 144, 85 to 145, 85 to 146, 85 to 147, 85 to 148, 85 to 149, 85 to 150, 85 to 151, 85 to 152, 85 to 153, 85 to 154, 85 to 155, 85 to 156, 85 to 157, 85 to 158, 85 to 159, 85 to 160, 85 to 161, 85 to 162, 85 to 163, 85 to 164, 85 to 165, 85 to 166, 85 to 167, 85 to 168, 85 to 169, 85 to 170, 85 to 171, 85 to 172, 85 to 173, 85 to 174, 85 to 175, 85 to 176, 85 to 177, 85 to 178, 85 to 179, 85 to 180, 85 to 181, 85 to 182, 85 to 183, 85 to 184, 85 to 185, 85 to 186, 85 to 187, 85 to 188, 85 to 189, 85 to 190, 85 to 191, 85 to 192, 85 to 193, 85 to 194, 85 to 195, 85 to 196, 85 to 197, 85 to 198, 85 to 199, 85 to 200, 85 to 201, 85 to 202, 85 to 203, 85 to 204, 85 to 205, 85 to 206, 85 to 207, 85 to 208, 85 to 209, 85 to 210, 85 to 211, 85 to 212, 85 to 213, 85 to 214, 85 to 215, 85 to 216, 85 to 217, 85 to 218, 85 to 219, 85 to 220, 85 to 221, 85 to 222, 85 to 223, 85 to 224, 85 to 225, 85 to 226, 85 to 227, 85 to 228, 85 to 229, 85 to 230, 85 to 231, 85 to 232, 85 to 233, 85 to 234, 85 to 235, 85 to 236, 85 to 237, 85 to 238, 85 to 239, 85 to 240, 85 to 241, 85 to 242, 85 to 243, 85 to 244, 85 to 245, 85 to 246, 85 to 247, 85 to 248, 85 to 249, 85 to 250, 85 to 251, 85 to 252, 85 to 253, 85 to 254, 85 to 255, 85 to 256, 85 to 257, 85 to 258, 85 to 259, 85 to 260, 85 to 261, 85 to 262, 85 to 263, 85 to 264, 85 to 265, 85 to 266, 85 to 267, 85 to 268, 85 to 269, 85 to 270, 85 to 271, 85 to 272, 85 to 273, 85 to 274, 85 to 275, 85 to 276, 85 to 277, 85 to 278, 85 to 279, 85 to 280, 85 to 281, 85 to 282, 85 to 283, 85 to 284, 85 to 285, 85 to 286, 85 to 287, 85 to 288, 85 to 289, 85 to 290, 85 to 291, 85 to 292, 85 to 293, 85 to 294, 85 to 295, 85 to 296, 85 to 297, 85 to 298, 85 to 299, 85 to 300, 85 to 301, 85 to 302, 85 to 303, 85 to 304, 85 to 305, 85 to 306, 85 to 307, 85 to 308, 85 to 309, 85 to 310, 85 to 311, 85 to 312, 85 to 313, 85 to 314, 85 to 315, 85 to 316, 85 to 317, 85 to 318, 85 to 319, 85 to 320, 85 to 321, 85 to 322, 85 to 323, 85 to 324, 85 to 325, 85 to 326, 85 to 327, 85 to 328, 85 to 329, 85 to 330, 85 to 331, 85 to 332, 85 to 333, 85 to 334, 85 to 335, 85 to 336, 85 to 337, 85 to 338, 85 to 339, 85 to 340, 85 to 341, 85 to 342, 85 to 343, 85 to 344, 85 to 345, 85 to 346, 85 to 347, 85 to 348, 85 to 349, 85 to 350, 85 to 351, 85 to 352, 85 to 353, 85 to 354, 85 to 355, 85 to 356, 85 to 357, 85 to 358, 85 to 359, 85 to 360, 85 to 361, 85 to 362, 85 to 363, 85 to 364, 85 to 365, 85 to 366, 85 to 367, 85 to 368, 85 to 369, 85 to 370, 85 to 371, 85 to 372, 85 to 373, 85 to 374, 85 to 375, 85 to 376, 85 to 377, 85 to 378, 85 to 379, 85 to 380, 85 to 381, 85 to 382, 85 to 383, 85 to 384, 85 to 385, 85 to 386, 85 to 387, 85 to 388, 85 to 389, 85 to 390, 85 to 391, 85 to 392, 85 to 393, 85 to 394, 85 to 395, 85 to 396, 85 to 397, 85 to 398, 85 to 399, 85 to 400, 85 to 401, 85 to 402, 85 to 403, 85 to 404, 85 to 405, 85 to 406, 85 to 407, 85 to 408, 85 to 409, 85 to 410, 85 to 411, 85 to 412, 85 to 413, 85 to 414, 85 to 415, 85 to 416, 85 to 417, 85 to 418, 85 to 419, 85 to 420, 85 to 421, 85 to 422, 85 to 423, 85 to 424, 85 to 425, 85 to 426, 85 to 427, 85 to 428, 85 to 429, 85 to 430, 85 to 431, 85 to 432, 85 to 433, 85 to 434, 85 to 435, 85 to 436, 85 to 437, 85 to 438, 85 to 439, 85 to 440, 85 to 441, 85 to 442, 85 to 443, 85 to 444, 85 to 445, 85 to 446, 85 to 447, 85 to 448, 85 to 449, 85 to 450, 85 to 451, 85 to 452, 85 to 453, 85 to 454, 85 to 455, 85 to 456, 85 to 457, or 85 to 458.

In the context of the present invention new and known substances have been examined in the assays according to the present invention. As a result thereof substances could be identified which can act as a Treg cell activator of the present invention, i.e. such a substance is able to activate a Treg cell via interaction with the Treg cell epitope as set forth in SEQ ID NO:1 which could be proven in vivo.

The Present Invention Therefore Provides for Treg Cell Activators.

Disclosed are Treg cell activators according to the invention which are structurally a peptide or a polypeptide, preferably an antibody of a binding fragment thereof or a scaffolded peptide.

The present invention further concerns a new antibody or a binding fragment thereof capable of binding to the peptide as set forth in SEQ ID NO.:1 with the proviso that the antibody or the antibody fragment is not OKT4A, OKT4D4, OKTcdr4a and not Leu3. Said disclaimed antibodies all relate to a totally different technical filed, namely HIV-1 research which is not related to the activation of Treg cells and disease according to the present invention. Even the present invention combines for the first time the technical field of (a) HIV-1 related diseases with (b) diseases according to the present invention e.g autoimmune disease, allergy, asthma, graft rejection and a diseases due to lacking immunotolerance caused by organ transplantation or by therapeutical administration of a non-self or self biological entity to a human in need thereof.

A further preferred Treg cell activator peptide is a peptide selected from a group consisting of a peptide comprising the amino acid sequence as set forth in SEQ ID NO.: 3, SEQ ID NO.: 4, SEQ ID NO.: 5, SEQ ID NO.: 6, SEQ ID NO.: 7, SEQ ID NO.: 8, SEQ ID NO.: 9, and SEQ ID NO.: 10, or is a peptide selected from a group consisting of a peptide consisting of the amino acid sequence as set forth in SEQ ID NO.: 3, SEQ ID NO.: 4, SEQ ID NO.: 5, SEQ ID NO.: 6, SEQ ID NO.: 7, SEQ ID NO.: 8, SEQ ID NO.: 9, and SEQ ID NO.: 10.

A more preferred Treg cell activator polypeptide is selected from a group consisting of: HIV-1 gp120, NSC 13778 which chemical structure is disclosed in Yang et al. 2005 on page 6124 in FIG. 1, peptide2 which presents three HIV-1 gp120 fragments bound together through conformationally flexible scaffolds which chemical structure is disclosed in Franke et al. 2007 on page 4 at the bottom of the right column, monoclonal antibody OKT4A which binds to the HIV-1 gp120-binding region of CD4 as disclosed in Mizukami et al. 1988 on page 9273 right column line 19, monoclonal antibody OKT4D which binds to the HIV-1 gp120-binding region of CD4 as disclosed in Mizukami et al. 1988 on page 9273 right column line 19, monoclonal antibody OKTcdr4a which derives from the murine OKT4a as disclosed in Moreland et al. 1998 on page 222 right column line 1, monoclonal antibody Leu3 which binds to epitope overlapping the HIV-1 gp120-binding site of CD4 as disclosed in Lohmann et al. 1992 on page 3248 left column line 7, and monoclonal antibody MAX.12H5 which binds to the CDR2-like region of CD4 as disclosed in Repke et al. 1992 on page 1809 abstract line 11 and on page 1812 left column line 37.

Each of the above mentioned Treg cell activators according to the present invention can be used as a medicament and for the preparation of a medicament for the treatment of a disease selected from a group consisting of (i) a non-autoimmune inflammatory disease: asthma, allergic asthma, respiratory allergy, allergic rhinoconjunctivitis, allergic alveolitis, contact allergy, atopic dermatitis, neurodermatitis, food allergy, graft-versus-host disease, non-autoimmune inflammatory bowel disease, acute respiratory distress syndrome, acute inflammatory pancreatitis, burns, wound healing, skin scarring disorders, sarcoidosis, Behcet's disease, Sweet's syndrome; (ii) an autoimmune inflammatory disease: rheumatoid arthritis, rheumatic fever, systemic lupus erythematosus, ulcerative colitis, Crohn's disease, autoimmune inflammatory bowel disease, diabetes type I, gastritis, autoimmune atrophic gastritis, autoimmune hepatitis, Hashimoto's thyroiditis, thyreoiditis, multiple sclerosis, myasthenia gravis, autoimmune haemolytic anemia, Addison's disease, scleroderma, Goodpasture's syndrome, Guillain-Barre syndrome, Graves' disease, glomerulonephritis, psoriasis, pemphigus vulgaris, pemphigoid, vitiligo, idiopathic leukopenia, Sjogren's syndrome, Wegener's granulomatosis; (iii) an inflammatory disease due to organ transplantation; (iv) a bone marrow transplantation; and (v) a disease due to exogenously administered self or exogenously administered non-autologous recombinant polypeptide.

An other embodiment of the present invention relates to a pharmaceutical composition comprising at least one Treg cell activator according to the present invention—preferably HIV-1 gp120—as an active ingredient and can be formulated in conventional manner. Methods for making such formulations can be found in manuals, e.g. “Remington Pharmaceutical Science”. Examples for ingredients that are useful for formulating at least one substance according to the present invention are also found in WO99/18193, which is hereby incorporated by reference. The composition may be manufactured in a manner that is itself known, e.g. by mean of conventional mixing, dissolving, granulating, dragee-making, levitating, powdering, emulsifying, encapsulating, entrapping of lyophilizing processes.

In a further aspect the invention teaches a method for treating a disease which is characterized in that its clinical picture can be influenced positively by an increase of activated Treg cells which method comprises administering to a being preferably a human being in need of such a treatment a suitable amount of a pharmaceutical composition comprising at least one Treg cell activator according to the present invention, preferably HIV-1 gp120 or HIV-1 gp120 derived fragments and peptides thereof. The present invention provides therefore for a method for treating (i) a non-autoimmune inflammatory disease: asthma, allergic asthma, respiratory allergy, allergic rhinoconjunctivitis, allergic alveolitis, contact allergy, atopic dermatitis, neurodermatitis, food allergy, graft-versus-host disease, non-autoimmune inflammatory bowel disease, acute respiratory distress syndrome, acute inflammatory pancreatitis, burns, wound healing, skin scarring disorders, sarcoidosis, Behcet's disease or Sweet's syndrome; (ii) an autoimmune inflammatory disease: rheumatoid arthritis, rheumatic fever, systemic lupus erythematosus, ulcerative colitis, Crohn's disease, autoimmune inflammatory bowel disease, diabetes type I, gastritis, autoimmune atrophic gastritis, autoimmune hepatitis, Hashimoto's thyroiditis, thyreoiditis, multiple sclerosis, myasthenia gravis, autoimmune haemolytic anemia, Addison's disease, scleroderma, Goodpasture's syndrome, Guillain-Barre syndrome, Graves' disease, glomerulonephritis, psoriasis, pemphigus vulgaris, pemphigoid, vitiligo, idiopathic leukopenia, Sjogren's syndrome or Wegener's granulomatosis; (iii) an inflammatory disease due to organ transplantation; (iv) a bone marrow transplantation; or (v) a disease due to exogenously administered self or exogenously administered non-autologous recombinant polypeptide which method comprises administering to a being in need of such a treatment a suitable amount of a pharmaceutical composition comprising at least one Treg cell activator.

The present invention additionally, provides for a use of a Treg cell activator according to the present invention for reducing and/or preventing an unwanted immune reaction due to a exogenously administered self or exogenously administered non-autologous recombinant polypeptide and provides for a method for reducing or preventing an unwanted immune reaction comprising: (a) adding a sufficient amount of at least one Treg cell activator according to the present invention to a non-human animal, preferably a non-human primate.

In a further embodiment the present invention provides for a test system for determining whether a substance is a Treg cell activator according to the present invention comprising at least

-   -   a) a Treg cell and     -   b) a peptide spanning at least the epitope as set forth in SEQ         ID NO.: 1

In a preferred test system of the present invention a peptide of b) is selected from a group consisting of an isolated peptide spanning amino acid No. 26 to 458 of SEQ ID NO.: 2, amino acid No. 26 to 419 of SEQ ID NO.: 2, amino acid No. 26 to 207 of SEQ ID NO.: 2, amino acid No. 26 to 131 of SEQ ID NO.: 2, and amino acid No. 46 to 89 of SEQ ID NO.: 2. or the peptide used is an isolated peptide spanning amino acid No. 1 to 31 of SEQ ID NO.: 1 and having additional up-stream and/or downstream amino acids with the prerequisite that the additional amino acids do not hinder binding of a substance to the amino acid stretch as set forth in SEQ ID No.:1. Said additional up-stream amino acid or amino acid stretch is preferably selected from a group consisting of the amino acid or amino acid stretch as set forth in SEQ ID NO.: 2 at position 53, at position 52-53, at position 51-53, at position 50-53, at position 49-53, at position 48-53, at position 47-53, at position 46-53, at position 45-53, at position 44-53, at position 43-53, at position 42-53, at position 41-53, at position 40-53, at position 39-53, at position 38-53, at position 37-53, at position 36-53, at position 35-53, at position 34-53, at position 33-53, at position 32-53, at position 31-53, at position 30-53, at position 29-53, at position 28-53, at position 27-53, at position 26-53, at position 25-53, at position 24-53, at position 23-53, at position 22-53, at position 21-53, at position 20-53, at position 19-53, at position 18-53, at position 17-53, at position 16-53, at position 15-53, at position 14-53, at position 13-53, at position 12-53, at position 11-53, at position 10-53, at position 9-53, at position 8-53, at position 7-53, at position 6-53, at position 5-53, at position 4-53, at position 3-53, at position 2-53, and at position 1-53. A more preferred peptide does additionally comprise downstream one or more amino acids as set forth in SEQ ID NO.: 2 at position 85, or at position 85 to n, wherein n is an integer between 86-458, i.e. position 85 to 86, 85 to 87, 85 to 88, 85 to 89, 85 to 90, 85 to 91, 85 to 92, 85 to 93, 85 to 94, 85 to 95, 85 to 96, 85 to 97, 85 to 98, 85 to 99, 85 to 100, 85 to 101, 85 to 102, 85 to 103, 85 to 104, 85 to 105, 85 to 106, 85 to 107, 85 to 108, 85 to 109, 85 to 110, 85 to 111, 85 to 112, 85 to 113, 85 to 114, 85 to 115, 85 to 116, 85 to 117, 85 to 118, 85 to 119, 85 to 120, 85 to 121, 85 to 122, 85 to 123, 85 to 124, 85 to 125, 85 to 126, 85 to 127, 85 to 128, 85 to 129, 85 to 130, 85 to 131, 85 to 132, 85 to 133, 85 to 134, 85 to 135, 85 to 136, 85 to 137, 85 to 138, 85 to 139, 85 to 140, 85 to 141, 85 to 142, 85 to 143, 85 to 144, 85 to 145, 85 to 146, 85 to 147, 85 to 148, 85 to 149, 85 to 150, 85 to 151, 85 to 152, 85 to 153, 85 to 154, 85 to 155, 85 to 156, 85 to 157, 85 to 158, 85 to 159, 85 to 160, 85 to 161, 85 to 162, 85 to 163, 85 to 164, 85 to 165, 85 to 166, 85 to 167, 85 to 168, 85 to 169, 85 to 170, 85 to 171, 85 to 172, 85 to 173, 85 to 174, 85 to 175, 85 to 176, 85 to 177, 85 to 178, 85 to 179, 85 to 180, 85 to 181, 85 to 182, 85 to 183, 85 to 184, 85 to 185, 85 to 186, 85 to 187, 85 to 188, 85 to 189, 85 to 190, 85 to 191, 85 to 192, 85 to 193, 85 to 194, 85 to 195, 85 to 196, 85 to 197, 85 to 198, 85 to 199, 85 to 200, 85 to 201, 85 to 202, 85 to 203, 85 to 204, 85 to 205, 85 to 206, 85 to 207, 85 to 208, 85 to 209, 85 to 210, 85 to 211, 85 to 212, 85 to 213, 85 to 214, 85 to 215, 85 to 216, 85 to 217, 85 to 218, 85 to 219, 85 to 220, 85 to 221, 85 to 222, 85 to 223, 85 to 224, 85 to 225, 85 to 226, 85 to 227, 85 to 228, 85 to 229, 85 to 230, 85 to 231, 85 to 232, 85 to 233, 85 to 234, 85 to 235, 85 to 236, 85 to 237, 85 to 238, 85 to 239, 85 to 240, 85 to 241, 85 to 242, 85 to 243, 85 to 244, 85 to 245, 85 to 246, 85 to 247, 85 to 248, 85 to 249, 85 to 250, 85 to 251, 85 to 252, 85 to 253, 85 to 254, 85 to 255, 85 to 256, 85 to 257, 85 to 258, 85 to 259, 85 to 260, 85 to 261, 85 to 262, 85 to 263, 85 to 264, 85 to 265, 85 to 266, 85 to 267, 85 to 268, 85 to 269, 85 to 270, 85 to 271, 85 to 272, 85 to 273, 85 to 274, 85 to 275, 85 to 276, 85 to 277, 85 to 278, 85 to 279, 85 to 280, 85 to 281, 85 to 282, 85 to 283, 85 to 284, 85 to 285, 85 to 286, 85 to 287, 85 to 288, 85 to 289, 85 to 290, 85 to 291, 85 to 292, 85 to 293, 85 to 294, 85 to 295, 85 to 296, 85 to 297, 85 to 298, 85 to 299, 85 to 300, 85 to 301, 85 to 302, 85 to 303, 85 to 304, 85 to 305, 85 to 306, 85 to 307, 85 to 308, 85 to 309, 85 to 310, 85 to 311, 85 to 312, 85 to 313, 85 to 314, 85 to 315, 85 to 316, 85 to 317, 85 to 318, 85 to 319, 85 to 320, 85 to 321, 85 to 322, 85 to 323, 85 to 324, 85 to 325, 85 to 326, 85 to 327, 85 to 328, 85 to 329, 85 to 330, 85 to 331, 85 to 332, 85 to 333, 85 to 334, 85 to 335, 85 to 336, 85 to 337, 85 to 338, 85 to 339, 85 to 340, 85 to 341, 85 to 342, 85 to 343, 85 to 344, 85 to 345, 85 to 346, 85 to 347, 85 to 348, 85 to 349, 85 to 350, 85 to 351, 85 to 352, 85 to 353, 85 to 354, 85 to 355, 85 to 356, 85 to 357, 85 to 358, 85 to 359, 85 to 360, 85 to 361, 85 to 362, 85 to 363, 85 to 364, 85 to 365, 85 to 366, 85 to 367, 85 to 368, 85 to 369, 85 to 370, 85 to 371, 85 to 372, 85 to 373, 85 to 374, 85 to 375, 85 to 376, 85 to 377, 85 to 378, 85 to 379, 85 to 380, 85 to 381, 85 to 382, 85 to 383, 85 to 384, 85 to 385, 85 to 386, 85 to 387, 85 to 388, 85 to 389, 85 to 390, 85 to 391, 85 to 392, 85 to 393, 85 to 394, 85 to 395, 85 to 396, 85 to 397, 85 to 398, 85 to 399, 85 to 400, 85 to 401, 85 to 402, 85 to 403, 85 to 404, 85 to 405, 85 to 406, 85 to 407, 85 to 408, 85 to 409, 85 to 410, 85 to 411, 85 to 412, 85 to 413, 85 to 414, 85 to 415, 85 to 416, 85 to 417, 85 to 418, 85 to 419, 85 to 420, 85 to 421, 85 to 422, 85 to 423, 85 to 424, 85 to 425, 85 to 426, 85 to 427, 85 to 428, 85 to 429, 85 to 430, 85 to 431, 85 to 432, 85 to 433, 85 to 434, 85 to 435, 85 to 436, 85 to 437, 85 to 438, 85 to 439, 85 to 440, 85 to 441, 85 to 442, 85 to 443, 85 to 444, 85 to 445, 85 to 446, 85 to 447, 85 to 448, 85 to 449, 85 to 450, 85 to 451, 85 to 452, 85 to 453, 85 to 454, 85 to 455, 85 to 456, 85 to 457, or 85 to 458.

The following examples are meant to illustrate the present invention, however, shall not be construed as limitation. However, the Examples describe most preferred embodiments of the invention.

EXAMPLES

(1) CD4/HIV-1 gp120 Competition Assay for Determining Whether a Substance can Bind at Least to a Peptide Spanning Epitope as Set Fourth in SEQ ID NO.:1

96 well assay plates (Nunc, Germany) are coated overnight at 4° C. with CD4 (sCD4, Immunodiagnostics, USA) 100 ng per well in PBS, pH 7.4. Coated plates are saturated with PBS/3% BSA buffer and washed three times. To determine binding of a test substance sample is added for 1 hour in different concentrations. No test substance is added to control wells. After washing three times HIV-1 gp120-peroxidase conjugate (Immunodiagnostics, USA) is added to the plate for 1 h. Unbound HIV-1 gp120-peroxidase conjugate is removed by washing three times After washing, 3,3,5,5-tetramethylbenzidine chromogen substrate (Pierce, USA) for peroxidase is added and the optical density is read at 450 nm. A substance which interacts with the CD4 HIV-1 gp120-binding site will block the binding of labeled HIV-1 gp120 and is identifiable by a reduced signal compared to the controls.

(2) Assay for Determining Whether E.G. HIV-1 gp120 or a Substance which can Interfere with HIV-1 gp120-Binding to a CD4⁺CD25⁺ Treg can Activate a CD4⁺CD25⁺ Treg and Therewith can be Useful in the Treatment an Autoimmune Disease (E.G. Inflammatory Bowel Disease, Multiple Sclerosis, Rheumatoid Arthritis, Psoriasis, Diabetes Type I, Lupus Erythematosus, Phemphigus Vulgaris, Thyreoiditis), Other Diseases with Autoimmune Aspects in their Pathogenesis Such as Vitiligo, Atopic Dermatitis, an Allergy (E.G. Allergic Rhinitis), Asthma (E.G. Allergic Asthma), GVHD (Graft-Versus-Host Disease), Graft Resection (2.1) Method for Isolation of Cells (2.1.1) Isolation of PBMC

The isolation procedure starts with PBMC (peripheral blood mononuclear cells) isolated by standard density gradient centrifugation from normal buffy coat preparations of healthy volunteers. Alternatively, PBMC isolated from whole peripheral blood or leukapheresis products can be used.

Blood from buffy coats is diluted 1:1 with PBS (phosphate buffered saline) containing 0.2% Liquemine (Sodium-Heparin) and 2 mM EDTA at room temperature. The diluted blood is thoroughly pipetted onto prepared Ficoll layers (30 ml diluted blood per 15 ml Ficoll layer per 50 ml tube) and centrifuged for 15 min. (minute) at 200×g (with brake on) at room temperature. 8-10 ml of the upper fluid are carefully removed and the tubes centrifuged at 450×g for 15 min. at room temperature (with brake off). PBMC are collected from the interphase of each gradient, washed three times with 50 ml PBS/1 mM EDTA separately, than pooled and wash two more times. Finally, PBMC are re-diluted in X-VIVO-15 (Cambrex, Verviers, Belgium) in cell culture medium and counted.

(2.1.2) Isolation of CD4⁺ T Helper Cells

For determining suppressive activity of Treg cells highly purified cell populations are needed. Therefore, antibody-coated magnetic beads are used (Miltenyi, Germany and or Dynal, Norway). Magnetic beads in this context are paramagnetic particles that are coupled to specific monoclonal antibodies. They are used to magnetically label the target cell population. The antibody-coated magnetic beads bind to the target cells. This labeled cell fraction is retained by magnetic force and can be recovered subsequently highly purified (positive selection). Before positive isolation of CD4⁺CD25⁻ T helper cells PBMC are washed two times with 50 ml washing buffer according to the manufacturer's instructions (Miltenyi Germany). For isolation of CD4⁺ T cells, CD4 microbeads (Miltenyi Germany, 2-4 μL microbeads/10⁷ PBMC) are used according to the manufacturer's instructions. The CD4⁺ fraction is isolated using a MACS separator (Miltenyi) according to the instructions of the manufacturer. MACS separator retains magnetic bead-labeled cells by magnetic force. Contaminating CD4⁺CD25⁺ Treg cells are depleted in a second step by using CD25 Dynabeads, (Dynal, Norway) according to the instructions of the manufacturer (details see 2.1.4) using (0.5 beads/cell). This depletion procedure results in highly purified CD4⁺CD25⁻ T helper cells (negative selection).

To circumvent CD4 antibodies binding to CD4⁺ cells (to avoid CD4-dependent pre-activation) in the isolation procedure of CD4⁺ T cells, alternatively untouched CD4⁺ T helper cells are generated by using the negative isolation kit (Miltenyi Germany) according to the manufacturer's instructions. Before negative isolation of CD4⁺ T helper cells PBMC are washed two times with 50 ml washing buffer according to the manufacturer's instructions (Miltenyi Germany). For isolation of CD4⁺ T helper cells, PBMC are incubated with a cocktail of biotinylated CD45RO, CD8, CD14, CD16, CD19, CD56, CD36, CD123, anti-TCRγ/δ, and CD235a antibodies. These cells are subsequently magnetically labeled with Anti-Biotin Microbeads for depletion. The CD4⁺ fraction is isolated using a MACS separator (Miltenyi) according to the instructions of the manufacturer. MACS separator retains magnetic bead-labeled cells by magnetic force. Contaminating CD4⁺CD25⁺ Treg cells are depleted in a second step by using CD25 Dynabeads, (Dynal, Norway) according to the instructions of the manufacturer (details see 2.1.4) using 0.5 beads/cell.

(2.1.3) Isolation of CD8⁺ T Effector Cells

Before positive isolation of CD8⁺ T effector cells PBMC are washed two times with 50 ml washing buffer according to the manufacturer's instructions (Miltenyi Germany). For isolation of CD8⁺CD25⁻ T-cells, CD8 microbeads (Miltenyi Germany, 2-4 μL microbeads/10⁷ PBMC) are used according to the manufacturer's instructions. The CD8⁺ fraction is isolated using a MACS separator (Miltenyi) according to the instructions of the manufacturer. Contaminating CD8⁺CD25⁺ T cells are depleted in a second step by using CD25 Dynabeads, (Dynal, Norway) according to the instructions of the manufacturer (details see 2.1.4) using (0.5 beads/cell). This depletion procedure results in highly purified CD8⁺CD25⁻ T effector cells (negative selection).

(2.1.4) Isolation of CD4⁺CD25⁺ Treg Cells

For Isolation of CD4⁺CD25⁺ Treg cells positive and negative selection is combined. PBMC are washed with washing buffer according to the manufacturer's instructions (Miltenyi Germany) and subsequently incubated with CD25 microbeads (2 μL microbeads/10⁷ PBMC) for 20 min. at 4° C. in isolation buffer (1×10⁸/ml) according to the manufacturer's instructions. Afterwards, the cells are washed two times in PBS. The CD25⁺ fraction is isolated using a MACS separator (Miltenyi) according to the instructions of the manufacturer. The positively selected CD25⁺ fraction contains 65-80% CD4⁺ T cells and 20-35% contaminating CD19⁺ B cells, CD8⁺ T cells, and few CD14⁺ monocytes. The contaminating cells are depleted with Dynabeads (Dynal, Norway). The following amounts of beads are used: CD19 Dynabeads: 2 beads/cell, CD8 Dynabeads: 3 beads/cell, CD14 Dynabeads: 1 bead/cell. Collected Dynabeads are washed two times in 15-ml tubes with depletion buffer using the magnetic particle concentrator (Dynal) according to the manufacturer's instructions. The CD25⁺ PBMC fraction (5×10⁷/ml) is added in depletion buffer and incubated for 20 min. at 4° C. on a shaker (sample mixer, Dynal). Contaminating cells are depleted according to the manufacturer's instructions by the use of the magnetic particle concentrator. For higher purity of CD4⁺CD25⁺ Treg cells Dynabeads depletion is repeated once (>98% after two rounds of depletion).

(2.1.5) Generation of Monocyte-Derived Dendritic Cells

Dendritic cells (DC) are generated from buffy coats of healthy volunteers. PBMC (2.1.6) are plated in 6-well tissue culture plates at a density of 15×10⁶ cells/well in 3 ml X-VIVO-15 (Cambrex, Verviers, Belgium) plus 1.5% heat-inactivated autologous plasma containing 800 U/ml GM-CSF (Leukomax; Novartis, Basel, Switzerland) and 1,000 U/ml IL-4 (Strathmann Biotec, Hamburg, Germany). Cultures are fed every other day (days 2, 4 and 6) by removing 1 ml of the medium and adding back 1 ml fresh medium with cytokines. On day 7, non-adherent cells were harvested and transferred to new 6 well plates and cultured further on in the presence of 10 ng/ml IL-1β, 10 ng/ml TNF-α, 1,000 U/ml IL-6 (all from Strathmann, Biotech, Germany) and 1 μg/ml PGE₂ (Pharmacia-Upjohn, Uppsala, Sweden). Mature CD83⁺ DC are harvested at day 9 of culture.

(2.1.6) Isolation of CD3-Depleted PBMC

T cells are depleted from PBMC with CD3 Dynabeads (Dynal, Norway) by using 0.5 beads/cell. Collected Dynabeads are washed two times in 15 ml tubes with depletion buffer using the magnetic particle concentrator (Dynal) according to the manufacturer's instructions. PBMC (5×10⁷/ml) are added in depletion buffer and incubated for 20 min. at 4° C. on a shaker (sample mixer, Dynal). CD3⁺ cells are depleted according to the manufacturer's instructions by the use of the magnetic particle concentrator resulting in a purity of >98% CD3⁻ PBMC.

(2.1.7) Isolation of Human CD25-Depleted PBMC

PBMC are isolated according to (2.1.1). CD25-expressing regulatory T cells in the PBMC preparation are depleted with CD25 Dynabeads (Dynal, Norway) according to the instructions of the manufacturer (details see 2.1.4) by using 0.5 beads/cell. Collected Dynabeads are washed two times in 15-ml tubes with depletion buffer using the magnetic particle concentrator (Dynal) according to the manufacturer's instructions. PBMC (5×10⁷/ml) are added in depletion buffer and incubated for 20 min. at 4° C. on a shaker (sample mixer, Dynal). CD25⁺ cells are depleted according to the manufacturer's instructions by the use of the magnetic particle concentrator resulting in a purity of >99% CD25-negative PBMC.

(2.2) Method for Testing Suppressive Activity of CD4⁺CD25⁺ Treg Cells

(2.2.1) Coculture Suppression Assay A: Mixed Leukocyte Reaction (MLR)

Cocultures of CD4⁺ T helper cells or CD8⁺ T effector cells with CD4⁺CD25⁺ Treg cells and allogeneic DC have to be performed to analyze the suppressive activity of CD4⁺CD25⁺ Treg cells on CD4⁺ T helper cells or CD8⁺ T effector cells. Therefore, 1×10⁵/well CD4⁺ T helper cells (2.1.2) or CD8⁺ T effector cells (2.1.3) are cocultured with different numbers of CD4⁺CD25⁺ Treg cells (2.1.4; ratio 1:1 to 1:4) and 1×10⁴/well DC in 96 well flat bottom culture plates in X-VIVO 15 (Cambrex, Verviers, Belgium) in the presence or absence of a CD4-binding compound e.g. HIV-1 gp120 (0.1-10 μg/ml). Mature dendritic cells (DC) generated as described (2.1.5) are from the same donor as CD4⁺CD25⁺ Treg cells (syngenic) but allogeneic to the CD4⁺ T helper cells or CD8⁺ T effector cells are used for T cell stimulation. In this assay, only CD4⁺ T helper cells or CD8⁺ T effector cells are activated by the allogeneic DC (MLR) resulting in a strong proliferation of the T cell subset. Non-activated CD4⁺CD25⁺ Treg cells did not suppress this proliferation in absence of a Treg cell activating compound. A functional activation of CD4⁺CD25⁺ Treg cells by a CD4-binding compound resulted in a reduced proliferation of CD4⁺ T helper cells or CD8⁺ T effector cells.

Proliferation is determined after 4 days of culture by adding 37 kBq 3H-Thymindine (3H-Tdr) for additional 16 h.

(2.2.2) Coculture Suppression Assay B: Stimulation of CD8⁺ T Effector Cells with Allogeneic PBMC and CD4⁺CD25⁺ Treg Cells from the Same Healthy Volunteer.

In order to study the influence of a substance, e.g. HIV-1 gp120 which can bind at least to the epitope given in SEQ ID NO.:1 exclusively on the suppressive function of CD4⁺CD25⁺ Treg cells, we developed a co-culture assay which contained CD8⁺ T cells as effectors to exclude any influence of this substance on the latter (CD8⁺ T cells don't express CD4). In this setting, activation of alloreactive CD8⁺ T effector cells is only suppressed by activated CD4⁺CD25⁺ Treg cells such as upon additional anti-CD3 mAb stimulation (positive control). To evaluate the influence of e.g. HIV-1 gp120 on the function of CD4⁺CD25⁺ Treg cells, isolated CD4⁺CD25⁺ Treg cells (2.1.4) are co-cultured with syngenic, T cell-depleted and irradiated (50 Gy) PBMC (2.1.6) and allogeneic CD8⁺ T effector cells (2.1.3) in presence of varying concentrations (0.1-10 μg/ml) of different HIV-1 gp120 preparations. Briefly, 1×10⁵ CD4⁺CD25⁺ Treg cells are incubated with 3×10⁵ syngenic T cell-depleted PBMC in the presence or absence of varying amounts of HIV-1 gp120. Stimulation with 0.5 μg/ml anti-CD3 monoclonal antibody (OKT-3, ebioscience, USA) serves as positive control. No additional stimulation represents negative control. Either immediately or 24 h later, 1×10⁵ allogeneic CD8⁺ T effector cells are added to the cultures and proliferation is determined after additional 72 h by ³H-Tdr incorporation (37 kBq/well). Functional activation of CD4⁺CD25⁺ Treg cells via interaction with the epitope as set forth in SEQ ID NO:1 result in suppressed proliferation of CD8⁺ T effector cells and therewith identifies a substance as a Treg cell activator (Data see FIG. 1).

To show in parallel whether a substance can interfere with HIV-1 gp120 binding to CD4 epitope of a CD4⁺CD25⁺ Treg cell, CD4 is added in different concentrations (0.1-10 μg/ml) to isolated CD4⁺CD25⁺ Treg cells (2.1.4) cocultured with syngenic T cell-depleted PBMC (2.1.6) and allogeneic CD8⁺ T effector cells (2.1.3) in the presence of varying amounts of the substance. Enhanced proliferation of CD8⁺effector cells resembles competitive binding to CD4 and blocked activation of a Treg cell via interaction with the epitope as set forth in SEQ ID NO:1. All cultures are performed in serum free X-VIVO-15 (Cambrex, Verviers, Belgium).

Alternatively to irradiation-induced inactivation and block of proliferation PBMC can be treated with Mitomycin C (Sigma, Germany). Briefly, 3×10⁷ PBMC are incubated in 3 ml MEM/10% FCS/180 μg Mitomycin C for 30 min at 37° C. Afterwards cells are washed 5× using MEM/10% FCS. Subsequently cells are subjected to the assay.

(2.2.3) Coculture Suppression Assay C: Stimulation of T Cells in Presence of Pre-Activated CD4⁺CD25⁺ Treg Cells and Allogeneic PBMC

To evaluate the direct Treg cell activating potential of a compound in the absence of antigen-presenting cells such as PBMC, isolated CD4⁺CD25⁺ Treg cells (according to 2.1.4) are pre-cultured in X-VIVO-15 for 16-48 h alone, in presence of 0.5 μg/ml anti-CD3 monoclonal antibody (OKT-3) as positive control, or in presence of different concentrations of HIV-1 gp120. Afterwards, cells are washed intensively and added to cocultures of syngenic, irradiated (50 Gy) PBMC and allogeneic CD4⁺ T helper cells or CD8⁺ T effector cells. Proliferation is determined after additional 72 h by ³H-Tdr incorporation (37 kBq/well). Functional activation of CD4⁺CD25⁺ Treg cells via interaction with the epitope as set forth in SEQ ID NO:1 result in suppressed proliferation of CD4⁺ T helper cells or CD8⁺ T effector cells and therewith identifies a substance as a Treg cell activator.

A reduced incorporated radioactivity resembles suppressed proliferation and identifies CD8⁺ inhibition and therewith identifies a substance to activate a Treg cell via interaction with the epitope as set forth in SEQ ID NO:1.

(2.3.) Method for Readout of Suppressive Activity of CD4⁺CD25⁺ Treg Cells

(2.3.1) Analysis of Proliferation

After 3-4 days of incubation of cells in assays provided under (2.2.1), (2.2.2) and (2.2.3) T cell proliferation is measured. For additional 16 h, cells are pulsed with ³H-Tdr (37 kBq/well, MB Biomedicals), and incorporated radioactivity is measured by using a liquid scintillation counter (Betaplate, Wallac/PerkinElmer). In the absence of a Treg cell activating compound, resting Treg cells cannot inhibit the proliferation of CD4⁺ T helper cells or CD8⁺ T effector cells (negative control). In contrast, in presence of an activating CD4-binding compound or anti-CD3 monoclonal antibody (positive control) the proliferation of CD4⁺ T helper cells or CD8⁺ T effector cells is suppressed by CD4⁺CD25⁺ Treg cells. A reduced incorporated radioactivity resembles suppressed proliferation and identifies CD4⁺ T helper cell or CD8⁺ T effector cell inhibition and therewith identifies that a CD4⁺CD25⁺ Treg cell has been activated.

For some experiments the proliferation of either CD4⁺CD25⁺ Treg cells, CD4⁺ T helper cells or CD8⁺ T effector cells is selectively followed by flow cytometry after labeling of these population with Vibrant CFDA SE Cell Tracer Kit (Invitrogen Life Technologies, San Diego, USA) according to the manufacturer's protocol. For CFDA labeling, T cells (1×10⁷ cells/ml) are incubated in PBS with 1 μM CFDA Vibrant CFDA SE Cell Tracer Kit (Invitrogen Life Technologies, San Diego, USA) at 37° C. for 30 min. Thereafter, cells are washed with X-VIVO-15 and incubated for 30 min. at 37° C. in the dark. After an additional wash the cells are counted and added to the cocultures. In addition, proliferation of cells is measured by flow cytometry after 4-6 days of culture.

(2.3.2) Analysis of Cytokine Production

Activated Treg cells not only inhibit the proliferation of cocultured CD4⁺ T helper cells or CD8⁺ T effector cells, they suppress also the cytokine synthesis of these T cells. Therefore, detection of cytokines produced by cocultured T cells is an alternative method to analyze the Treg cell activating potential of a reagent. In this assay, isolated CD4⁺CD25⁺ Treg cells (according to 2.1.4), syngenic CD3-depleted PBMC (according to 2.1.6) and allogeneic CD8⁺ T effector cells (according to 2.1.3) are cocultured as described (2.2) before. After 7 days, alloreactive CD8⁺ T effector cells are polyclonal restimulated with 2.4 μg/ml phytohemagglutinin (PHA, Sigma, Germany) and 1 ng/ml PMA for 5 h in presence of monensin (BD GolgiStop™, BD Biosciences Pharmingen 1.3 μM). Thereafter, cells are collected, washed with PBS, fixed and permeabilized according to the manufacturer's instruction (perm/fix solution, BD PharMingen, Germany) and stained with 0.5 μg/test of a cytokine-specific monoclonal antibody (anti-IFN-γ, anti-IL-2, anti-TNF-α, all from BD PharMingen). Subsequently, production of cytokines by CD4⁺ T helper cells or CD8⁺ T effector cells is analyzed by flow cytometry. In the absence of a Treg cell activating compound Treg cells cannot inhibit the cytokine production of CD4⁺ T helper cells or CD8⁺ T effector cells (negative control). In contrast, in presence of an activating CD4-binding compound or anti-CD3 monoclonal antibodies (positive control) the cytokine production of CD4⁺ T helper cells or CD8⁺ T effector cells is suppressed by functional activated Treg cells. A reduced cytokine production identifies inhibition and therewith identifies that a CD4⁺CD25⁺ Treg cell has been activated.

(2.3.3) Analysis of CD25 Expression

Activated Treg cells inhibit the ability of CD8⁺ T effector cells and CD4⁺ T helper cells to express the α-chain of the IL-2 receptor, CD25. Therefore, the analysis of CD25 expression by flow cytometry is an additional method to evaluate the Treg cell activating potential of a reagent. In this assay, isolated CD4⁺CD25⁺ Treg cells (according to 2.1.4) and syngenic CD3-depleted PBMC (according to 2.1.6) are cocultured with allogeneic CD8⁺ T effector cells or allogeneic CD4⁺ T helper cells (according to 2.1.3, 2.1.2 and 2.2.1, 2.2.2 and 2.2.3). After 7 days, alloreactive CD8⁺ T effector cells or allogeneic CD4⁺ T helper cells are stimulated with allogeneic PBMC from the same donor or DC as used in primary culture and expression of CD25 on alloreactive CD8⁺ T effector or allogeneic CD4⁺ T helper cells are analyzed 24 h thereafter by flow cytometry. Activation of Treg cells by the test compound results directly in an inhibited CD25 expression on the re-stimulated CD8⁺ T effector cells or CD4⁺ T helper cells. In the absence of a Treg cell activating compound, Treg cells cannot inhibit the CD25 expression on re-stimulated CD8⁺ T effector cells or CD4⁺ T helper cells (negative control). In contrast, in presence of an activating reagent or an anti-CD3 monoclonal antibody (positive control) the CD25 expression of CD8⁺ T effector cells or CD4⁺ T helper cells is suppressed by Treg cells. A reduced CD25 expression identifies inhibition and therewith identifies that a CD4⁺CD25⁺ Treg cell has been activated.

(2.3.4) Analysis of Cyclic AMP Production

Stimulation of Treg cells results in strong increase of cytosolic (i.e intracellular) cAMP. Therefore, the analysis of cAMP in Treg cells is an additional method to determine whether a substance which can interfere with HIV-1 gp120 binding to CD4 epitope of a CD4-positive cell can activate a Treg cell. In this assay freshly isolated CD4⁺CD25⁺ Treg cells (according to 2.1.4) (1×10⁵-1×10⁶/well) are incubated with anti-CD3 monoclonal antibody (OKT-3; 0.5 μg/ml) or HIV-1 gp120 (0.1-10 μg/ml; Protein Science Corp., Meriden, Conn., USA) or left untreated for 16 hours. To assess cytosolic cAMP-concentrations a cAMP-specific ELISA (Parameter™ Cyclic AMP Assay, Cat. No. KGE002; R&D Systems, Wiesbaden, Germany) is applied. Treg cells are washed three times in ice-cold PBS and subsequently lysed (1×10⁷/ml) using lysis buffer supplied by the manufacturer and applied to the ELISA according to the manufacturer's recommendations.

Activation of Treg cells by the test compound results directly in an increase of cytosolic cAMP. In the absence of a Treg cell activating compound no increase of cAMP in CD4⁺CD25⁺ Treg cells is detected (negative control). In contrast, in presence of an activating CD4-binding compound or an anti-CD3 monoclonal antibody (positive control) CD4⁺CD25⁺ Treg cell show a strong increase of cytosolic cAMP. An increase of cytosolic cAMP identifies that a CD4⁺CD25⁺ Treg cell has been activated. Data see FIG. 2.

Alternatively, additional analysis of assay supernatant cAMP concentration and use of phoshodiesterase inhibitors e.g. Roflumilast (1-50 μM) enhance the cAMP signal in the assay.

(3) In Vivo Assay for Determining Whether HIV-1 gp120 or a Substance which can Interfere with HIV-1 gp120-Binding to a CD4⁺CD25⁺ Treg can Activate a CD4⁺CD25⁺ Treg in a Disease-Related Model and Therewith can be Useful in the Treatment of an Autoimmune Disease (e.g. Inflammatory Bowel Disease, Multiple Sclerosis, Rheumatoid Arthritis, Psoriasis, Diabetes Type I, Lupus Erythematosus, Phemphigus Vulgaris, Thyreoiditis), Other Diseases with Autoimmune Aspects in their Pathogenesis such as Vitiligo, Atopic Dermatitis, an Allergy (e.g. Allergic Rhinitis), Asthma (e.g. Allergic Asthma), GVHD (Graft-Versus-Host Disease), Graft Resection (3.1) Method for Induction of GVHD by Transfer of Human PBMC into NOD-Scid Mice and Measurement of Disease Severity.

NOD-Scid mice, non-obese diabetic/severe combined immunodeficient mice (mutant allele: Prkdc^(scid), strain: NOD.CB17-Prkdc^(scid), (Shultz et al 1995)) from the Central Laboratory Animal Facility of the University of Mainz (also purchasable from The Jackson Laboratory via Charles River Laboratories, Germany) are used as an animal model for transfer of peripheral human immune cells and thus for the in vivo analysis of immuno-regulatory interactions (Hesselton et al. 1995). Human peripheral blood mononuclear cells (PBMC) transferred into NOD-Scid mice induce an accelerating age-dependent graft-versus-host disease (GVHD). While the number of cells transferred determines the onset of this disease, the co-transfer of human Tregs can gradually delay or prevent the disease. This model system further allows the study of human Treg function. To induce a GVHD NOD-Scid mice at the age of three to six days after birth are intraperitoneally injected with 1×10⁷ to 3×10⁷ human PBMC (isolation of human PBMC according to 2.1.1). GVHD is induced by immunological (xenogenic) activation of human effector T cells in the PBMC fraction injected into the mice. NOD-Scid mice, however, are not able to react against the grafted human PBMC. The human PBMC-induced disease is characterized by lack of weight increase and weight loss, decreased mobility, hunched posture, ruffled fur and organ inflammation in the treated animals (Kizilisik and Al-Sebayel 1997). Transfer of human PBMC results in growth arrest or weight loss within 30 to 40 days (depending on the number of cells transferred) after transfer compared to untreated mice. Lack of weight increase/weight loss is used as a parameter to score GVHD severity. Control mice did not receive any PBMC. Data see FIG. 3.

(3.2) Method for Induction of GVHD by Transfer of Human PBMC into Nod-Scid Mice and Prevention of Disease by Additional Transfer of Human Regulatory T Cells and Measurement of Disease Severity.

To prevent a GVHD disease in NOD-Scid mice at the age of three to six days after birth induced by intraperitoneally injection of 1×10⁷ to 3×10⁷ human PBMC (isolation of human PBMC according to 2.1.1) additional 2.5×10⁶ human regulatory T cells (isolation of human regulatory T cells according to 2.1.4) are injected intraperitoneally (ratio Tregs to PBMC: 1:4). Co-transfer of human regulatory T cells along with human PBMC (enhancement of Treg ratio) results in prevention of development of GVHD and weight loss similar development as untreated mice. Lack of weight increase/weight loss is used as a parameter to score GVHD severity. Control mice did not receive any PBMC. Data see FIG. 3.

(3.3) Method for Induction of GVHD by Transfer of Human PBMC into Nod-Scid Mice and Prevention of Disease by Additional Administration of HIV-1 gp120 or a Substance which can Interfere with HIV-1 gp120-Binding and Measurement of Disease Severity.

To prevent a GVHD disease induced in NOD-Scid mice at the age of three to six days after birth induced by intraperitoneally injection of 1×10⁷ to 3×10⁷ human PBMC (isolation of human PBMC according to 2.1.1) HIV-1 gp120 or a substance which can interfere with HIV-1 gp120-binding is administered in addition to the injection of human PBMC. Administration of HIV-1 gp120 or a substance which can interfere with HIV-1 gp120-binding induces an activation of human regulatory T cells in the PBMC fraction resulting in prevention of organ inflammation and prevention of growth arrest/weight loss similar to mice treated with human PBMC and additional human regulatory T cells or untreated mice. Lack of weight increase/weight loss is used as a parameter to score GVHD severity. Control mice did not receive any PBMC. Data see FIG. 4.

(3.4) Method for Induction of GVHD by Transfer of Human PBMC into Nod-Scid Mice and to Demonstrate that Prevention of Disease by Administration of HIV-1 gp120 or a Substance which can Interfere with HIV-1 gp120-Binding is Mediated by Human Regulatory T Cells in the PBMC Fraction Injected into Nod-Scid Mice and Measurement of Disease Severity.

NOD-Scid mice at the age of three to six days after birth are intraperitoneally injected with 1×10⁷ human CD25-depleted PBMC (isolation of human CD25-depleted PBMC according to 2.1.7). GVHD is induced by 1×10⁷ human CD25-depleted PBMC at the same magnitude as by transfer of 1×10⁷ human non CD25-depleted PBMC into NOD-Scid mice. (Data see FIG. 5 and FIG. 3 and FIG. 4) Mice receiving CD25-depleted PBMC and an additional administration of HIV gp120 are not protected from development of GVHD and weight loss. Prevention of GVHD by HIV gp120 or a substance which can interfere with HIV-1 gp120-binding depends on regulatory T cells. Lack of weight increase/weight loss is used as a parameter to score GVHD severity. Data see FIG. 5.

DESCRIPTION OF FIGURES

FIG. 1: HIV-1 gp120 Treatment Activates Human CD4⁺CD25⁺ Treg Cells

In order to study the influence of HIV-1 gp120 exclusively on the function of CD4⁺CD25⁺ Treg cells, we developed a coculture assay which contained CD8⁺ T cells as effectors to exclude any influence of HIV-1 gp120 on the latter. Therefore, isolated CD4⁺CD25⁺ Treg cells are cocultured with T cell-depleted syngenic PBMC and allogeneic CD8⁺ T effector cells. In this setting, proliferation of alloreactive CD8⁺ T effector cells is only suppressed by activated CD4⁺CD25⁺ Treg cells such as upon additional anti-CD3 mAb stimulation or an activating HIV-1 gp120-mediated signal. (All HIV-1 gp120 proteins: Protein Sciences Corp. Meriden, USA)

1×10⁵ isolated CD25⁺ Treg cells were incubated with 3×10⁵ irradiated (50 Gy) syngenic T cell-depleted PBMC and 1×10⁵ allogeneic CD8⁺ T effector cells in presence/absence of different HIV-1 gp120 preparations, addition of 0.5 μg/ml anti-CD3 (OKT-3) served as positive control. Proliferation was determined by ³H-Tdr-Incorporation 4 days later.

Grey bars represent proliferation of CD8⁺ T cells and inactivated syngenic CD3-depleted PBMC, white bars represent the proliferation of CD4⁺CD25⁺ Tregs and the black bars represent the proliferation of CD8⁺ T cells co-cultured with CD4⁺CD25⁺ Tregs cells and inactivated syngenic CD3-depleted PBMC. Due to inactivation PBMC don't contribute to proliferation of the samples.

As can be seen by the low white bars, Tregs don't show a significant proliferation under all conditions (without additional stimulus, or anti-CD3, or HIV-1 gp120 MN, or HIV-1 gp120 LAV, or HIV-1 gp120 CM). CD8⁺ T cells (grey bars) and CD8⁺ T cells co-cultured with Treg cells (black bars) show the same magnitude of proliferation under the condition without additional stimulus representing the controls. Upon anti-CD3 stimulation CD8⁺ T cells (grey bars) show strong increased proliferation but CD8⁺ T cells co-cultured with Treg cells (black bars) show a reduced proliferation indicating suppressed proliferation of CD8⁺ T cells by anti-CD3 activated and therefore suppressive Tregs. The effect is anti-CD3 dose-dependent. Upon stimulation with HIV-1 gp120 MN, or HIV-1 gp120 LAV, or HIV-1 gp120 CM CD8⁺ T cells co-cultured with Treg cells (black bars) in contrast to CD8⁺ T cells without Tregs (grey bars) reduced proliferation indicating HIV-1 gp120 activated Tregs. This demonstrates clearly that HIV-1 gp120 activates Tregs which subsequently exert suppressive activity on CD8⁺ T cells by reducing their proliferation. The suppressive activity of Treg cells and therefore the reduced proliferation is HIV-1 gp120 dose-dependent.

FIG. 2: Cyclic AMP Measurement in CD4⁺CD25⁺ Treg Cells

HIV-1 gp120 Treatment Augments Cytosolic Camp in Human CD4⁺CD25⁺ Treg Cells

CD4⁺CD25⁺ regulatory T cells (CD25) are left untreated (ø) or stimulated with an anti-CD3 monoclonal Antibody (OKT-3; 1 μg/ml) or HIV-1 gp120 (1 μg/ml). Upon 16 hours of stimulation the CD4⁺CD25⁺ regulatory T cells are lysed (1×10⁷/ml) and the cytosolic cAMP concentration of 1×10⁶ T cells is assessed using a cAMP-specific ELISA.

CD4⁺CD25⁺ regulatory T cells (CD25) are left untreated (ø) or stimulated with an anti-CD3 monoclonal Antibody (OKT-3; 1 μg/ml) or HIV-1 gp120 (1 μg/ml). Upon 16 hours of stimulation the CD4⁺CD25⁺ regulatory T cells are lysed (1×10⁷/ml) and the cytosolic cAMP concentration of 1×10⁶ T cells is assessed using a cAMP-specific ELISA.

Bars represent the amount of cytosolic (intracellular) cyclic AMP (cAMP) in untreated Treg cells or Treg cells treated with different stimuli. The upper bar represent Tregs left untreated (ø) and shows the basal level of intracellular cAMP. Upon anti-CD3 stimulation (OKT-3) Tregs are activated and show an increase of intracellular cAMP compared to the untreated control (upper bar) as demonstrated with the second bar. Treatment of Tregs with HIV-1 gp120 also induces an increase of intracellular cAMP as demonstrated with the lower bar. This demonstrated that activation of Treg cells with different stimuli induces an increase of cytosolic cAMP which can be used as readout for activation.

FIG. 3: Induction of GVHD by Transfer of PBMC into NOD-Scid Mice and Prevention of GVHD by Additional Transfer of Regulatory T Cells (Tregs).

Three to six days old NOD-Scid mice are intraperitoneally injected with 1×10⁷ human PBMC without (circles) or together with 2.5×10⁶ human regulatory T cells (triangles). Control mice (rhombi) did not receive any PBMC. Mice having received PBMC develop a fatal GVHD, do not grow and die. Animals having additionally received regulatory T cells are protected from development of GVHD and develop normally (3 mice per group). Lack of weight increase/weight loss is used as a parameter to score GVHD severity. The diagram shows the relative body weight at different time points after transfer.

FIG. 4: Induction of GVHD by Transfer of PBMC into Nod-Scid Mice and Prevention of GVHD by Additional Injection of HIV gp120.

Three to six days old NOD-Scid mice are intraperitoneally injected with 1×10⁷ human PBMC without (circles) or together with 5 μg HIV gp120 (triangles). Control mice (rhombs) did not receive any PBMC. Mice having received PBMC develop a fatal GVHD, do not grow and die. Animals having additionally received HIV gp120 are protected from development of GVHD and develop normally (3 mice per group). Lack of weight increase/weight loss is used as a parameter to score GVHD severity. The diagram shows the relative body weight at different time points after transfer.

FIG. 5: Prevention of GVHD in Nod-Scid Mice Transferred with PBMC by Additional Injection of HIV gp120 Depends on the Presence of Regulatory T Cells.

Three to six days old NOD-Scid mice are intraperitoneally injected with 1×10⁷ human CD25-depleted PBMC without (circles) or together with 5 μg HIV gp120 (triangles). Control mice (rhombi) do not receive any PBMC (3 mice per group). Mice having received CD25-depleted PBMC develop a fatal GVHD, do not grow and die. Animals having received 1×10⁷ human CD25-depleted PBMC and additionally HIV gp120 are not protected from development of GVHD, also do not grow and die. Lack of weight increase/weight loss is used as a parameter to score GVHD severity. The diagram shows the relative body weight at different time points after transfer.

LITERATURE

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The invention claimed is:
 1. A method for determining whether a substance can activate a Treg cell via interaction with the HIV-1 gp120-binding site of CD4, comprising: (a) pre-selecting a substance which can interact with the HIV-1 gp120-binding site of CD4, (b) providing a solution comprising a CD4⁺CD25⁺ Treg cell, (c) adding a pre-selected substance according to (a) under conditions which allow interaction of the substance with a CD4⁺CD25⁺ Treg cell, (d) measuring whether a CD4⁺CD25⁺ Treg cell has been activated, wherein an activated CD4⁺CD25⁺ Treg cell identifies the substance as a Treg cell activator.
 2. A method according to claim 1 wherein a Treg cell is a Tr1 cell or a Th3 cell.
 3. A method according to claim 1 wherein in (b) of claim 1 a solution is provided which comprises (i) a CD4⁺CD25⁺ Treg cell, (ii) an inactivated syngenic CD3-depleted PBMC (peripheral blood mononuclear cell) or a dendritic cell (DC) and (iii) an allogeneic CD8⁺ T cell or an allogeneic CD4⁺ T cell.
 4. A method according to claim 3 wherein the inactivated syngenic CD3-depleted PBMC has been inactivated via irradiation or via mitomycin C.
 5. A method according to claim 3 wherein the measuring of whether a CD4⁺CD25⁺ Treg cell has been activated is determined by measuring whether a CD8⁺ T cell has been suppressed, wherein a suppressed CD8⁺ T cell identifies an activated CD4⁺CD25⁺Treg cell and therewith identifies the substance as a Treg cell activator.
 6. A method according to claim 5 wherein measuring whether a CD8⁺ T cell has been suppressed is determined by measuring inhibited proliferation of the CD8⁺ T cell or by measuring reduced CD25 expression of the CD8⁺ T cell.
 7. A method according to claim 5 wherein measuring whether a CD8⁺ T cell has been suppressed is determined by measuring inhibited cytokine production of the CD8⁺ T cell.
 8. A method according to claim 7 wherein the cytokine is IFNγ or IL2 or TNF-α.
 9. A method according to claim 3 wherein the measuring of whether a CD4⁺CD25⁺ Treg cell has been activated is determined by measuring whether a CD4⁺ T cell has been suppressed, wherein a suppressed CD4⁺ T cell identifies an activated CD4⁺CD25⁺ Treg cell and therewith identifies the substance as a Treg cell activator.
 10. A method according to claim 9 wherein measuring whether a CD4⁺ T cell has been suppressed is determined by measuring inhibited proliferation of the CD4⁺ T cell or by measuring reduced CD25 expression of the CD4⁺ T cell.
 11. A method according to claim 9 wherein measuring whether a CD4⁺ T cell has been suppressed is determined by measuring inhibited cytokine production of the CD4⁺ T cell.
 12. A method according to claim 11 wherein the cytokine is IFNγ or IL2 or TNF-α.
 13. A method according to claim 1 wherein in (d) of claim 16 the measuring whether a CD4⁺CD25⁺ Treg cell has been activated is determined by measuring the amount of intracellular cAMP and wherein an increased amount of intracellular cAMP is indicative for an activated CD4⁺CD25⁺ Treg cell and therewith identifies the substance as a Treg cell activator.
 14. A method according to claim 1 wherein step (a) of claim 16 comprises: (a) providing a first solution comprising CD4, (b) providing a second solution comprising CD4, (c) adding to the first solution a substance to be tested and HIV-1 gp120 under conditions which allow binding of HIV-1 gp120 with CD4, (d) adding to the second solution HIV-1 gp120 under conditions like (c) allowing binding of HIV-1 gp120 with CD4, (e) measuring in the first and in the second solution whether the HIV-1 gp120 has bound to the CD4 wherein a reduced amount of bound HIV-1 gp120 in the first solution indicates that the substance can interact with HIV-1 gp120-binding site of CD4.
 15. A method according to claim 14 wherein instead of CD4 a peptide is used which comprises the amino acid stretch as set forth in SEQ ID NO.1.
 16. A method according to claim 15 wherein instead of CD4 a peptide is used as set forth in SEQ ID NO.1.
 17. A method according to claim 14 wherein instead of HIV-1 gp120 a peptide is used selected from a group consisting of a peptide comprising the amino acid sequence as set forth in SEQ ID NO.: 3, SEQ ID NO.: 4, SEQ ID NO.: 5, SEQ ID NO.: 6, SEQ ID NO.: 7, SEQ ID NO.: 8, SEQ ID NO.: 9, and SEQ ID NO.:
 10. 18. A method according to claim 14 wherein instead of HIV-1 gp120 a peptide is used selected from a group consisting of a peptide consisting of the amino acid sequence as set forth in SEQ ID NO.: 3, SEQ ID NO.: 4, SEQ ID NO.: 5, SEQ ID NO.: 6, SEQ ID NO.: 7, SEQ ID NO.: 8, SEQ ID NO.: 9, and SEQ ID NO.:
 10. 19. A method for determining whether a substance can activate a regulatory T cell (Treg) via interaction with the epitope as set forth in SEQ ID NO: 1 comprising: (a) providing a first solution comprising a CD4⁺CD25⁺ Treg cell, (b) adding a substance to be tested under conditions which allow interaction of the substance with a CD4⁺CD25⁺ Treg cell, (c) measuring whether a CD4⁺CD25⁺ Treg cell of the first solution has been activated, (d) providing a second solution comprising a CD4⁺CD25⁺ Treg cell, (e) adding the substance to be tested and a peptide comprising an amino acid sequence as set forth in SEQ ID NO: 1 under conditions like (b), (f) measuring whether a CD4⁺CD25⁺ Treg cell of the second solution has been activated, (g) comparing results obtained from (c) with those obtained from (f) wherein a reduced activation of (f) identifies the substance as a Treg cell activator which activates a CD4⁺CD25⁺ Treg cell via interaction with the epitope as set forth in SEQ ID NO:
 1. 20. A method according to claim 19 wherein in step (e) of claim 34 the peptide used is selected from a group consisting of an isolated peptide spanning amino acid No. 1-31 of SEQ ID NO 1, No. 26 to 458 of SEQ ID NO.: 2, No. 26 to 419 of SEQ ID NO.:2, No. 26 to 207 of SEQ ID NO.: 2, No. 26 to 131 of SEQ ID NO.: 2 and No. 46 to 89 of SEQ ID NO.:
 2. 21. A method according to claim 19 wherein in step (e) of claim 34 the peptide used is an isolated peptide spanning amino acid No. 1 to 31 of SEQ ID NO.: 1 and having additional up-stream and/or downstream amino acids with the prerequisite that the additional amino acids do not hinder binding of a substance to the amino acid stretch as set forth in SEQ ID No.:
 1. 22. A method according to claim 21 wherein the additional up-stream amino acid or amino acid stretch is selected from a group consisting of the amino acid or amino acid stretch as set forth in SEQ ID NO.: 2 at position 53, at position 52-53, at position 51-53, at position 50-53, at position 49-53, at position 48-53, at position 47-53, at position 46-53, at position 45-53, at position 44-53, at position 43-53, at position 42-53, at position 41-53, at position 40-53, at position 39-53, at position 38-53, at position 37-53, at position 36-53, at position 35-53, at position 34-53, at position 33-53, at position 32-53, at position 31-53, at position 30-53, at position 29-53, at position 28-53, at position 27-53, at position 26-53, at position 25-53, at position 24-53, at position 23-53, at position 22-53, at position 21-53, at position 20-53, at position 19-53, at position 18-53, at position 17-53, at position 16-53, at position 15-53, at position 14-53, at position 13-53, at position 12-53, at position 11-53, at position 10-53, at position 9-53, at position 8-53, at position 7-53, at position 6-53, at position 5-53, at position 4-53, at position 3-53, at position 2-53, and at position 1-53.
 23. A method according to claim 21 wherein additional downstream amino acids are given in SEQ ID NO.: 2 at position 85, or at position 85 to n, wherein n is an integer between 86-458.
 24. A method according to claim 19 wherein a Treg cell is a Tr1 cell or a Th3 cell.
 25. A method according to claim 19 wherein in (a) and (d) of claim 19 a solution is provided which comprises (i) a CD4⁺CD25⁺ Treg cell, (ii) an inactivated syngenic CD3-depleted PBMC (peripheral blood mononuclear cell) or a dendritic cell (DC) and (iii) an allogeneic CD8⁺ T cell or an allogeneic CD4⁺ T cell.
 26. A method according to claim 25 wherein the inactivated syngenic CD3-depleted PBMC has been inactivated via irradiation or via mitomycin C.
 27. A method according to claim 25 the measuring of whether a CD4⁺CD25⁺ Treg cell has been activated is determined by measuring whether a CD8⁺ T cell has been suppressed, wherein a suppressed CD8⁺ T cell identifies an activated CD4⁺CD25⁺ Treg cell and therewith identifies the substance as a Treg cell activator.
 28. A method according to claim 27 wherein measuring whether a CD8⁺ T cell has been suppressed is determined by measuring inhibited proliferation of the CD8⁺ T cell or by measuring reduced CD25 expression of the CD8⁺ T cell.
 29. A method according to claim 27 wherein measuring whether a CD8⁺ T cell has been suppressed is determined by measuring inhibited cytokine production of the CD8⁺ T cell.
 30. A method according to claim 29 wherein the cytokine is IFNγ or IL2 or TNF-α.
 31. A method according to claim 25 wherein the measuring of whether a Treg cell has been activated is determined by measuring whether a CD4⁺ T cell has been suppressed, wherein a suppressed CD4⁺ T cell identifies an activated CD4⁺CD25⁺ Treg cell and therewith identifies the substance as a Treg cell activator.
 32. A method according to claim 31 wherein measuring whether a CD4⁺ T cell has been suppressed is determined by measuring inhibited proliferation of the CD4⁺ T cell or by measuring reduced CD25 expression of the CD4⁺ T cell.
 33. A method according to claim 31 wherein measuring whether a CD4⁺ T cell has been suppressed is determined by measuring inhibited cytokine production of the CD4⁺ T cell.
 34. A method according to claim 33 wherein the cytokine is IFNγ or IL2 or TNF-α.
 35. A method according to claim 19 wherein the measuring of whether a Treg cell has been activated is determined by measuring the amount of intracellular cAMP and wherein an increased amount of intracellular cAMP is indicative for an activated Treg cell and therewith identifies the substance as a Treg cell activator. 